f_uac2: increase number of requests to 32 for UAC2

Increase number of requests for UAC2 driver from 2 to 32 to reduce
missed isoc events with isochronous endpoints.

Change-Id: I918f4c9564f1697fd69f135f38f3fc116b3c0900
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>