dmaengine: cppi: fix build error due to bad variable

Commit 8e3ba95f ("dmaengine: cppi41: use managed functions devm_*()")
moved the code to devm_* but erranously changed a varible name, so fix it.

drivers/dma/cppi41.c:1052:5: error: 'struct cppi41_dd' has no member named 'qmrg_mem'
  cdd->qmrg_mem = devm_ioremap_resource(dev, mem);
     ^
drivers/dma/cppi41.c:1053:16: error: 'struct cppi41_dd' has no member named 'qmrg_mem'
  if (IS_ERR(cdd->qmrg_mem))
                ^
drivers/dma/cppi41.c:1054:21: error: 'struct cppi41_dd' has no member named 'qmrg_mem'
   return PTR_ERR(cdd->qmrg_mem);
                     ^

Fixes: 8e3ba95f ("dmaengine: cppi41: use managed functions devm_*()")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>