dmaengine: sun4i: fix invalid argument

The "pchans_used" field is an unsigned long array.

for_each_clear_bit_from() expects an unsigned long pointer,
not an array address.

$ make C=2 drivers/dma/sun4i-dma.o
  CHECK   drivers/dma/sun4i-dma.c
drivers/dma/sun4i-dma.c:241:9: warning: incorrect type in argument 1 (different base types)
drivers/dma/sun4i-dma.c:241:9:    expected unsigned long const *p
drivers/dma/sun4i-dma.c:241:9:    got unsigned long ( *<noident> )[1]

Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>