defconfig: msm8960: Disable USB Storage debug config

when USB_STORAGE_DEBUG config is enabled, all scsi commands sent to
USB storage devices are printed onto console.  As serial console
is enabled, this is degrading throughput.  This debug feature is
useful only during debugging issues.  Hence disable this feature
by default.

CRs-Fixed: 421411
Change-Id: Ia475fb260b427fa85d241b8bb04503688d502f0e
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>