usb: u_bam: increase data rx queue size

The hardware controller can actually serve a larger number of requests at
once. This will reduce the overhead of queueing the requests to the
endpoint and improve cpu usage noticably while consuming only slightly
more memory.

Change-Id: Iddc25048f2ce50255ef36b50e883b3baf3e4e718
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>