ASoC: intel: make function stub static

This function stub should have been 'static' in the original patch
so that multiple uses of the header file (in different drivers)
will not cause multiple function definitions.

sound/soc/intel/boards/built-in.o: In function `sst_acpi_find_name_from_hid':
(.text+0x560): multiple definition of `sst_acpi_find_name_from_hid'
sound/soc/intel/atom/built-in.o:(.text+0x10610): first defined here
../scripts/Makefile.build:369: recipe for target 'sound/soc/intel/built-in.o' failed

Fixes: f17131a9: add function stub when ACPI is not enabled

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Mark Brown <broonie@kernel.org>