fsldma: print correct IRQ on mpc83xx

The mpc83xx variant uses a shared IRQ for all channels, so the individual
channel nodes don't have an interrupt property. Fix the code to print the
controller IRQ instead if there isn't any for the channel.

Acked-by: Timur Tabi <timur@freescale.com>
Acked-by: Li Yang <leoli@freescale.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>