USB: msm72k_otg: disable BAM mode

In BAM mode, USB core does posted writes on AHB bus, when it moves
the received setup packet to the memory. This might lead HW to fail in
copying the setup packet into the memory, before software reads. This
leads data corruption in setup packet and might lead USB re-enumeration.

If we don't use BAM mode for USB, then we should explicitly disable
the USB BAM mode by setting bit-13 of USB_GEN_CONFIG register. This
would prevent posted writes and resolves the above issue.

Signed-off-by: Chandra Devireddy <cdevired@codeaurora.org>