spirv: don't assert with location decorations on non i/o variables
spirv: don't assert with location decorations on non i/o variables

Some applications might add location decoration to samplers. Rather
than raising an error it seems it would make more sense to just
discard these decorations.

Signed-off-by: Lionel Landwerlin <9463032a5b99ffad10f36631678a833369a311b5@intel.com>
Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Cc: 17.0 <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler