USB: f_uac1: Increase the IN endpoint buffer allocation

Some UDC may require allocation of some extra bytes for
TX buffer due to hardware requirement. Add necessary
changes for the same.

Change-Id: I3e9fb4adfabff4b3d3742a76ded3c54ac464cf30
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>