usb: gadget: f_accessory: Enabled Zero Length Packet (ZLP) for acc_write

Accessory connected to Android Device requires
Zero Length Packet (ZLP) to be written when data
transferred out from the Android device are multiples
of wMaxPacketSize (64bytes (Full-Speed) / 512bytes (High-Speed))
to end the transfer.

Change-Id: Ib2c2c0ab98ef9afa10e74a720142deca5c0ed476
Signed-off-by: Anson Jacob <ansonkuzhumbil@gmail.com>

idea is taken here - https://github.com/rmbq/android_kernel_htc_msm8960/commit/5136bb3a12fa06f7a3f3d78315540a232682d45b