USB: Set AHB HPROT Mode to allow posted data writes

Currently writing 0x0 into AHBMODE register which means both data
transactions and QH and TD descriptors are non-posted writes to
system memory. As per HW team recommendation, should write 0x08 value
to set AHB HPROT mode into the AHBMODE register which allows posted
data writes to system memory and will improve the throughput numbers.

Change-Id: Ib44a8cfe11c6ff96ff712643227532e24548e706
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
[sboyd: Only the echi-msm.c part]