fsldma: check for NO_IRQ in fsl_dma_chan_remove()

There's no per-channel IRQ on mpc83xx, so only call free_irq if we have one.

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>