platform: msm: Fix uninitialized compiler warning in usb_bam

 drivers/platform/msm/usb_bam.c:385:20: error:
   'data_fifo_size' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Change-Id: Ic0dedbadfad2543ecd9baebc27abcf1befe55597
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>