[ Upstream commit 9a6bed4f ]

If the caller passes in a NULL cap_reservation, and we can't allocate
one then ensure that we fail gracefully.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>