docs-rst: fix usb cross-references

As some USB documentation files got moved, adjust their
cross-references to their new place.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/usb/URB.rst

@@ -1,3 +1,5 @@
+.. _usb-urb:
+
 USB Request Block (URB)
 ~~~~~~~~~~~~~~~~~~~~~~~
 

Documentation/driver-api/usb/callbacks.rst

@@ -8,7 +8,7 @@ Usbcore will call into a driver through callbacks defined in the driver
 structure and through the completion handler of URBs a driver submits.
 Only the former are in the scope of this document. These two kinds of
 callbacks are completely independent of each other. Information on the
-completion callback can be found in Documentation/usb/URB.txt.
+completion callback can be found in :ref:`usb-urb`.
 
 The callbacks defined in the driver structure are:
 
@@ -53,7 +53,7 @@ The callbacks defined in the driver structure are:
 
 The ioctl interface (2) should be used only if you have a very good
 reason. Sysfs is preferred these days. The PM callbacks are covered
-separately in Documentation/usb/power-management.txt.
+separately in :ref:`usb-power-management`.
 
 Calling conventions
 ===================

Documentation/driver-api/usb/error-codes.rst

@@ -1,3 +1,5 @@
+.. _usb-error-codes:
+
 USB Error codes
 ~~~~~~~~~~~~~~~
 

Documentation/driver-api/usb/persist.rst

@@ -1,3 +1,5 @@
+.. _usb-persist:
+
 USB device persistence during system suspend
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

Documentation/driver-api/usb/power-management.rst

@@ -328,7 +328,7 @@ possible to work around the hibernation-forces-disconnect problem by
 using the USB Persist facility.)
 
 The ``reset_resume`` method is used by the USB Persist facility (see
-``Documentation/usb/persist.txt``) and it can also be used under certain
+:ref:`usb-persist`) and it can also be used under certain
 circumstances when ``CONFIG_USB_PERSIST`` is not enabled.  Currently, if a
 device is reset during a resume and the driver does not have a
 ``reset_resume`` method, the driver won't receive any notification about

Documentation/driver-api/usb/usb.rst

@@ -424,8 +424,8 @@ header.
 Unless noted otherwise, the ioctl requests described here will update
 the modification time on the usbfs file to which they are applied
 (unless they fail). A return of zero indicates success; otherwise, a
-standard USB error code is returned. (These are documented in
-``Documentation/usb/error-codes.txt`` in your kernel sources.)
+standard USB error code is returned (These are documented in
+:ref:`usb-error-codes`).
 
 Each of these files multiplexes access to several I/O streams, one per
 endpoint. Each device has one control endpoint (endpoint zero) which