dma: mv_xor: use resource_size()

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Dan Williams <dan.j.williams@intel.com> (supporter:ASYNCHRONOUS TRAN...)
Cc: Vinod Koul <vinod.koul@intel.com> (supporter:DMA GENERIC OFFLO...)
Signed-off-by: Vinod Koul <vinod.koul@intel.com>