glsl: do not raise uninitialized warning with out function parameters

glsl: do not raise uninitialized warning with out function parameters

It silence by default warnings with function parameters, as the
parameters need to be processed in order to have the actual and the
formal parameter, and the function signature. Then it raises the
warning if needed at verify_parameter_modes where other in/out/inout modes
checks are done.

v2: fix comment style, multi-line condition style, simplify check,
    remove extra blank (Ian Romanick)
v3: inout function parameters can raise the warning too (Ian
    Romanick)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>