ASoC: wm_adsp: fix possible memory leak in wm_adsp_load_coeff()

'file' is malloced in wm_adsp_load_coeff() and should be freed
before leaving from the error handling cases, otherwise it will cause
memory leak.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>