USB: gadget: Initialize ci13xxx gadget device's coherent DMA mask

dma_alloc_coherent() which is internally called by dma_pool_alloc()
flags a warning if device's coherent DMA mask.  Hence initialize
gadget device's coherent DMA mask to it's parent mask.

Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>