usb: gadget: f_uvc: Enable high bandwidth transfers

Enable high bandwidth transfers on Video Streaming Isoc
IN endpoint for f_uvc driver by setting the module parameter
streaming_maxpacket to 3072. This will enable mult transactions
on the Video Streaming Isoc IN endpoint.
Fix the buffer size calculation of each USB request as the
earlier calculation doesn't work for endpoints with mult
transactions enabled.

CRs-fixed: 2043149
Change-Id: Id7d4a5aeb73c0152e4e41ce8d7c71956ea290ebc
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>