Android: fix spirv_info.c generation

Android: fix spirv_info.c generation

It's incorrect to use $(LOCAL_PATH) in makefile recipes since it's
changing. The typical way to handle it is to use private variable.
Fortunately in this case we can just simplify them to $^.

See further:
https://patchwork.freedesktop.org/patch/167718/

Also simplify LOCAL_GENERATED_SOURCES.

Fixes: 2dd4e2ec (spirv: Generate spirv_info.c)

Signed-off-by: Chih-Wei Huang <cwhuang@linux.org.tw>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>