Revert "cxgb3: Check and handle the dma mapping errors"

This reverts commit f83331ba.

As the tests PPC64 (powernv platform) show, IOMMU pages are leaking
when transferring big amount of small packets (<=64 bytes),
"ping -f" and waiting for 15 seconds is the simplest way to confirm the bug.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Santosh Rastapur <santosh@chelsio.com>
Cc: Jay Fenlason <fenlason@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Divy Le ray <divy@chelsio.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>