mesa: Fix glGetVertexAttribI[u]iv now that we have real integer attribs.

mesa: Fix glGetVertexAttribI[u]iv now that we have real integer attribs.

Since cf438f5375e242, we store actual integers for the attribute data.
We just need to reinterpret the GLfloat array as a GLint/GLuint array
so we can read the proper data.

Fixes oglconform's glsl-vertex-attrib/basic.VertexAttribI[1234][u]i
subtests (after fixing an unrelated bug in those test cases).

v2: Use the COPY_4V macro to be concise.

NOTE: This is a candidate for the stable branches.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Marek Olšák <maraeo@gmail.com> [v1]