dmaengine: ppc4xx: Convert to use sysfs_emit()/sysfs_emit_at() APIs

Follow the advice of the Documentation/filesystems/sysfs.rst and show()
should only use sysfs_emit() or sysfs_emit_at() when formatting the
value to be returned to user space.

Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Link: https://lore.kernel.org/r/202212061714501297954@zte.com.cn


Signed-off-by: Vinod Koul <vkoul@kernel.org>