net/mlx5e: Return in default case statement in tx_post_resync_params

clang warns:

drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:251:2:
warning: variable 'rec_seq_sz' is used uninitialized whenever switch
default is taken [-Wsometimes-uninitialized]
        default:
        ^~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:255:46: note:
uninitialized use occurs here
        skip_static_post = !memcmp(rec_seq, &rn_be, rec_seq_sz);
                                                    ^~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:239:16: note:
initialize the variable 'rec_seq_sz' to silence this warning
        u16 rec_seq_sz;
                      ^
                       = 0
1 warning generated.

This case statement was clearly designed to be one that should not be
hit during runtime because of the WARN_ON statement so just return early
to prevent copying uninitialized memory up into rn_be.

Fixes: d2ead1f3 ("net/mlx5e: Add kTLS TX HW offload support")
Link: https://github.com/ClangBuiltLinux/linux/issues/590


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>