ASoC: wm_adsp: Fixup wm_adsp2_boot_work error paths

Currently we are not disabling MEM_ENA on the error path, we should
really do this to unwind the state back to how it was. This patch adds a
clear of MEM_ENA on the error path, again there is no major issues
caused by this minor fix.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>