DMA: PL330: Check the pointer returned by kzalloc

commit 61c6e7531d3b66b33187b8cdd700fd8ab93ffd62 upstream.

kzalloc could return NULL. Hence add a check to avoid
NULL pointer dereference.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>