staging: mt7621-mmc: Fix dma_alloc_coherent should get device as first param

The dma_alloc_coherent (and also dma_free_coherent) should get the
device, the dma memory is allocated for as the first parameter.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>