intel/vec4: Remove leftover code from Gen8+ removal.

Remove code missed in commit 2a490074 ("intel/vec4: Remove all support for Gen8+ [v2]").

Fix defect reported by Coverity Scan.

Logically dead code (DEADCODE) dead_error_begin: Execution cannot reach this statement: mcs.swizzle = 80U;

Signed-off-by: Vinson Lee vlee@freedesktop.org

cc: @idr