block: sunvdc: add check for mdesc_grab() returning NULL

stable inclusion
from stable-v5.10.176
commit 2f28cb5c2a510185fec4a52e9ca20d78ce72f57d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8CHVQ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f28cb5c2a510185fec4a52e9ca20d78ce72f57d



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[ Upstream commit 60303631 ]

In vdc_port_probe(), we should check the return value of mdesc_grab() as
it may return NULL, which can cause potential NPD bug.

Fixes: 43fdf274 ("[SPARC64]: Abstract out mdesc accesses for better MD update handling.")
Signed-off-by: Liang He <windhl@126.com>
Link: https://lore.kernel.org/r/20230315062032.1741692-1-windhl@126.com


[axboe: style cleanup]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>