RDMA/cma: Remove NULL check before dev_{put, hold}

The call netdev_{put, hold} of dev_{put, hold} will check NULL, so there
is no need to check before using dev_{put, hold}, remove it to silence the
warning:

./drivers/infiniband/core/cma.c:4812:2-9: WARNING: NULL check before dev_{put, hold} functions is not needed.

Link: https://lore.kernel.org/r/20230614014328.14007-1-yang.lee@linux.alibaba.com


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5521


Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>