android: spirv: fix '::' typo in gen rules

android: spirv: fix '::' typo in gen rules

among all Android gen rules '::' was used only here to declare dependencies;
mesa development and stable branch are worth receiving the fix

Fixes the following building errors with Android 7:

obj/STATIC_LIBRARIES/libmesa_nir_intermediates/spirv/gl_spirv.P:184: *** target file
gen/STATIC_LIBRARIES/libmesa_nir_intermediates/spirv/vtn_generator_ids.h' has both : and :: entries.  Stop.

Cc: "20.3" <mesa-stable@lists.freedesktop.org>
Fixes: 1070bba19e26 ("android: fix SPIR-V -> NIR build")
Reported-by: youling257 <youling257@gmail.com>