dma: use BUG_ON correctly in ppc4xx/adam.c, v4

dma: use BUG_ON correctly in ppc4xx/adam.c, v4

This patch makes BUG_ON() usage correct in drivers/dma/ppc4xx/adam.c

Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Sean MacLennan <smaclennan@pikatech.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Coly Li <bosong.ly@taobao.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>