USB: android: override bcdDevice only if userspace passes it

The composite driver assigns the bcdDevice field in the device
descriptor to the current kernel version. Android composite driver
is overriding this with the default value 0xFFFF. Override bcdDevice
only if the userspace passes a value by writing into
/sys/class/android_usb/android0/bcdDevice file.

Change-Id: I19c62754ea6ae59a71a6aa472964f1a9f622c8e5
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>