glsl: Extract explicit location code from apply_type_qualifier_to_variable

glsl: Extract explicit location code from apply_type_qualifier_to_variable

Future patches will add some extra code to this path, and some of that
code will want to exit from the explicit location code early.

v2: Change a geometry shader "break" to a "return" so that try to apply
a bogus geometry shader location qualifier (which could cause cascading
errors).  Suggested by Paul.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>