dmaengine: usb-dmac: make usb_dmac_get_current_residue unsigned

dmaengine: usb-dmac: make usb_dmac_get_current_residue unsigned

The usb_dmac_get_current_residue function used to
take a signed integer as a pos parameter.
The only callers of this function passes an unsigned integer to it.
Therefore to make it obviously safe, let's just make this an unsgined
integer as this is used in pointer arithmetics.

Signed-off-by: Jordy Zomer <jordy@pwning.systems>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20210731091939.510816-1-jordy@pwning.systems
Signed-off-by: Vinod Koul <vkoul@kernel.org>