usb: gadget: f_uvc: Fix video streaming quality issues

The current UVC driver has quality issues because of
the requests' trbs missing isoc intervals.
Fix this by increasing the number of USB requests so
as to keep up with the hardware.

Change-Id: I6dfd11d79ac42c421f452e4be024dad86b7e0a97
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>