ASoC: qcom: rename rdmactl_audif_start to dmactrl_audif_start

This patch renames rdmactl_audif_start to dmactrl_audif_start as this
is common for both rdma and wrdma. Without this patch the name would be
bit misleading to the readers.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>