UVC: Increase usb requests for better throughput

Currently UVC driver is using 4 usb requests for data transfers.
Increase number of usb requests to 8 to improve throughput in UVC
driver.

Change-Id: Iea94a1c62e6c615cc88c4cc9f3a53e3719642e0f
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>