ASoC: atmel: test wrong variable

After clk_get() mclk is checked second time instead of pllb check.
In patch v1 Jarkko Nikula noticed that PTR_ERR() is also has wrong argument.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>