mesa: merge the prog_src_register::NegateBase and NegateAbs fields

There's really no need for two negation fields.  This came from the
GL_NV_fragment_program extension.  The new, unified Negate bitfield applies
after the absolute value step.

src/mesa/state_tracker/st_cb_bitmap.c

@@ -147,7 +147,7 @@ make_bitmap_fragment_program(GLcontext *ctx, GLuint samplerIndex)
       p->Instructions[ic].SrcReg[0].Swizzle = SWIZZLE_XXXX;
 
    p->Instructions[ic].SrcReg[0].Index = 0;
-   p->Instructions[ic].SrcReg[0].NegateBase = NEGATE_XYZW;
+   p->Instructions[ic].SrcReg[0].Negate = NEGATE_XYZW;
    ic++;
 
    /* END; */