RDMA/mlx5: Remove NULL check before dev_{put, hold}

Coccinelle reports a warning

WARNING: NULL check before dev_{put, hold} functions is not needed

The reason is the call netdev_{put, hold} of dev_{put,hold} will check NULL
There is no need to check before using dev_{put, hold}

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Link: https://lore.kernel.org/r/ZjGC4qXrOwZE0aHi@octinomon.home


Signed-off-by: Leon Romanovsky <leon@kernel.org>