glsl: Set default precision on record members

glsl: Set default precision on record members

Record types have their own slot to store the precision for each
member in glsl_struct_field. Previously if the member didn’t have an
explicit precision qualifier this was being left as
GLSL_PRECISION_NONE. This patch makes it take into account the type’s
default precision qualifier like it does for regular variables in
apply_type_qualifier_to_variable.

This has the additional benefit of correctly reporting an error when a
float type is used in a struct without declaring the default type.

Reviewed-by: Eric Anholt <eric@anholt.net>