dmaengine: img-mdc: remove unused ‘prev_phys’

In mdc_prep_dma_memcpy(), mdc_prep_dma_cyclic() and mdc_prep_slave_sg()
variable ‘prev_phys’ is initialized but never used, which
leads to warning with W=1

drivers/dma/img-mdc-dma.c: In function ‘mdc_prep_dma_memcpy’:
drivers/dma/img-mdc-dma.c:295:24: warning: variable ‘prev_phys’ set but not used [-Wunused-but-set-variable]
  dma_addr_t curr_phys, prev_phys;

drivers/dma/img-mdc-dma.c: In function ‘mdc_prep_dma_cyclic’:
drivers/dma/img-mdc-dma.c:378:24: warning: variable ‘prev_phys’ set but not used [-Wunused-but-set-variable]
  dma_addr_t curr_phys, prev_phys;

drivers/dma/img-mdc-dma.c: In function ‘mdc_prep_slave_sg’:
drivers/dma/img-mdc-dma.c:461:24: warning: variable ‘prev_phys’ set but not
used [-Wunused-but-set-variable]
  dma_addr_t curr_phys, prev_phys;

So remove it.

Cc: Damien.Horsley <Damien.Horsley@imgtec.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>