Revert "usb: host: Verify sg before accessing it in qh_urb_transaction"

This reverts commit 1d239e70
This change was causing -ENOMEM issue. It seems that the "break"
from the infinite loop only happens in the if (this_sg_len <= 0) check,
which does not get hit when adding the "sg &&" portion.
 This led to DMA pool exhaustion due to calling ehci_qtd_alloc()
many times and eventually to ENOMEM error.

Change-Id: If899c0eb0ec33b1b96c6e6592f95a4788b6c854a
Signed-off-by: Lena Salman <esalman@codeaurora.org>