ASoC: mediatek: Fix an error checking code

Check the value returned by 'devm_clk_get()' instead of the clock
identifier which can never be an ERR code.

Fixes: d6f3710a

 ("ASoC: mediatek: add structure define and clock control for 2701")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>