Fix the following sparse warning.

drivers/dma-buf/dma-heap.c:109:14: warning: symbol 'dma_heap_ioctl_cmds'
was not declared. Should it be static?
Acked-by: Andrew F. Davis <afd@ti.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
 [sumits: rebased over IOCTL rename patches]
Link: https://patchwork.freedesktop.org/patch/msgid/20191217190822.1969-1-sumit.semwal@linaro.org