docs: get rid of :c:type explicit declarations for structs

The :c:type:`foo` only works properly with structs before
Sphinx 3.x.

On Sphinx 3.x, structs should now be declared using the
.. c:struct, and referenced via :c:struct tag.

As we now have the automarkup.py macro, that automatically
convert:
	struct foo

into cross-references, let's get rid of that, solving
several warnings when building docs with Sphinx 3.x.

Reviewed-by: André Almeida <andrealmeid@collabora.com> # blk-mq.rst
Reviewed-by: Takashi Iwai <tiwai@suse.de> # sound
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/fpga/fpga-bridge.rst

@@ -4,8 +4,8 @@ FPGA Bridge
 API to implement a new FPGA bridge
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-* struct :c:type:`fpga_bridge` — The FPGA Bridge structure
-* struct :c:type:`fpga_bridge_ops` — Low level Bridge driver ops
+* struct fpga_bridge — The FPGA Bridge structure
+* struct fpga_bridge_ops — Low level Bridge driver ops
 * devm_fpga_bridge_create() — Allocate and init a bridge struct
 * fpga_bridge_register() — Register a bridge
 * fpga_bridge_unregister() — Unregister a bridge