i965: fix bogus swizzle in brw_cubemap_normalize
When used with a cube array in VS, failed assertion in ir_validate:
Assignment count of LHS write mask channels enabled not
matching RHS vector size (3 LHS, 4 RHS).
To fix this, swizzle the RHS correctly for the writemask.
This showed up in the ARB_texture_gather tests, which exercise cube
arrays in the VS.
Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: "9.2" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>