fs-verity: fix all kerneldoc warnings

Fix all kerneldoc warnings in fs/verity/ and include/linux/fsverity.h.
Most of these were due to missing documentation for function parameters.

Detected with:

    scripts/kernel-doc -v -none fs/verity/*.{c,h} include/linux/fsverity.h

This cleanup makes it possible to check new patches for kerneldoc
warnings without having to filter out all the existing ones.

Link: https://lore.kernel.org/r/20200511192118.71427-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/verity/enable.c

@@ -329,6 +329,8 @@ rollback:
 
 /**
  * fsverity_ioctl_enable() - enable verity on a file
+ * @filp: file to enable verity on
+ * @uarg: user pointer to fsverity_enable_arg
  *
  * Enable fs-verity on a file.  See the "FS_IOC_ENABLE_VERITY" section of
  * Documentation/filesystems/fsverity.rst for the documentation.