USB: android: increase MAX_STREAMING_FUNCS value to 6

Android gadget driver checks whether number of streaming
functions passed are less than MAX_STREAMING_FUNCS. Increase
this value from 3 to 6 as USB driver now uses more than 3
streaming functions.

Change-Id: Iaed07baad3b7d39e1500ee45ee99016378ba00a8
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>