lima/ppir: set write mask for texture loads if dest is reg

lima/ppir: set write mask for texture loads if dest is reg

Destination for texture load can be a reg, so we need to
set write mask in this case

Tested-by: Andreas Baierl <ichgeh@imkreisrum.de>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Reviewed-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>