dmaengine: stm32-dma: remove unused ‘src_addr’

In stm32_dma_set_xfer_param(), variable ‘src_addr’ is initialized but never used, which
leads to warning with W=1

drivers/dma/stm32-dma.c: In function ‘stm32_dma_set_xfer_param’:
drivers/dma/stm32-dma.c:577:13: warning: variable ‘src_addr’ set but not used [-Wunused-but-set-variable]
  dma_addr_t src_addr, dst_addr;

So remove it.

Reviewed-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>