i965: Don't assume that WPOS is always provided on gen6 in the new FS.

We sensibly only provide it if the FS asks for it.  We could actually
skip WPOS unless the FS needed WPOS.zw, but that's something for
later.

Fixes: glsl-texture2d and probably many others.

src/mesa/drivers/dri/i965/brw_fs.cpp

@@ -2258,8 +2258,7 @@ fs_visitor::calculate_urb_setup()
    /* Figure out where each of the incoming setup attributes lands. */
    if (intel->gen >= 6) {
       for (unsigned int i = 0; i < FRAG_ATTRIB_MAX; i++) {
-	 if (i == FRAG_ATTRIB_WPOS ||
-	     (brw->fragment_program->Base.InputsRead & BITFIELD64_BIT(i))) {
+	 if (brw->fragment_program->Base.InputsRead & BITFIELD64_BIT(i)) {
 	    urb_setup[i] = urb_next++;
 	 }
       }