dmaengine: ste_dma40: off by one in d40_of_probe()

If "num_disabled" is equal to STEDMA40_MAX_PHYS (32) then we would write
one space beyond the end of the pdata->disable_channels[] array.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>