block/brd: add error handling support for add_disk()

block/brd: add error handling support for add_disk()

[ Upstream commit e1528830bd4ebf435d91c154e309e6e028336210 ]

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20211015235219.2191207-2-mcgrof@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 67205f80be99 ("brd: mark as nowait compatible")
Signed-off-by: Sasha Levin <sashal@kernel.org>