soc: xtensa: intel_adsp: cavs: fix incorrect cached/uncached cast

Converting between cached and uncached aliases should have correct
sparse annotations. Fix following sparse warning:

/zep_workspace/zephyr/soc/xtensa/intel_adsp/cavs/power.c:97:53: warning:
incorrect type in argument 1 (different address spaces)

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>