ASoC: ti: omap-dmic: Fix IS_ERR() vs NULL check bug in omap_dmic_select_fclk()

ASoC: ti: omap-dmic: Fix IS_ERR() vs NULL check bug in omap_dmic_select_fclk()

clk_get_parent() returns NULL when the clock has no parent (or when the
input clk is NULL); it never returns an ERR_PTR. The current IS_ERR(mux)
check therefore never triggers - a NULL return falls through silently
to clk_set_parent(NULL, parent_clk), which simply fails with -EINVAL.

Use a NULL check so the dedicated error path runs and the prior
clk_get() reference is released via clk_put().

Signed-off-by: Ingyu Jang <ingyujang25@korea.ac.kr>
Acked-by: Sen Wang <sen@ti.com>
Link: https://patch.msgid.link/20260514185215.3753998-1-ingyujang25@korea.ac.kr
Signed-off-by: Mark Brown <broonie@kernel.org>