mesa: set Q=1 for OPCODE_TEX execution

mesa: set Q=1 for OPCODE_TEX execution

Q should not be significant for OPCODE_TEX, but it winds up getting
passed to the compute_lambda() function.  Make sure it's 1.0 to
prevent garbage values, which is effectively what we get when the
swizzle is coord.xyzz (which is what GLSL gives us).

Part of the fix for piglit's fbo-generatemipmap-array test.

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