ASoC: sti: Fix error handling if of_clk_get() fails

We intended to return here.  The current code has a static checker
warning because we set "ret" but don't use it.

Fixes: 76c2145d ("ASoC: sti: Add CPU DAI driver for playback")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Arnaud POULIQUEN <arnaud.pouliquen@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>