Remove unreached code in drivers/net/mlx4/en_rx.c

Remove the return after the goto.  We want the goto because it frees
memory as well as returning err.

Found by smatch (http://repo.or.cz/w/smatch.git).

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>