dmaengine: qcom_hidma: remove unused code

Fix the following clang warning:

drivers/dma/qcom/hidma.c:94:20: warning: unused function 'to_hidma_desc'
[-Wunused-function].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1617270816-36400-1-git-send-email-jiapeng.chong@linux.alibaba.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>