dmaengine: shdma: SH_DMAC_MAX_CHANNELS message fix

Fix the recently added SH_DMAC_MAX_CHANNELS handling code in
300e5f97 dmaengine: shdma: Fix SH_DMAC_MAX_CHANNELS handling

Without this fix the shdma driver outputs silly messages in
case SH_DMAC_MAX_CHANNELS happens to match the platform data:

sh-dma-engine sh-dma-engine.0: Attempting to register 20 DMA channels when a max
imum of 20 are supported.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>