glsl/linker: Properly error check VS-GS linkage.

glsl/linker: Properly error check VS-GS linkage.

From section 4.3.4 (Inputs) of the GLSL 1.50 spec:

    Geometry shader input variables get the per-vertex values written
    out by vertex shader output variables of the same names. Since a
    geometry shader operates on a set of vertices, each input varying
    variable (or input block, see interface blocks below) needs to be
    declared as an array.

Therefore, the element type of each geometry shader input array should
match the type of the corresponding vertex shader output.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>