net/mlx5e: Convert single case statement switch statements into if statements

During the review of commit 1ff2f0fa

 ("net/mlx5e: Return in default
case statement in tx_post_resync_params"), Leon and Nick pointed out
that the switch statements can be converted to single if statements
that return early so that the code is easier to follow.

Suggested-by: Leon Romanovsky <leon@kernel.org>
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>