Replace magic values with named constants when reading the TX chip from VGACRD1. Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20240916082920.56234-3-tzimmermann@suse.de