amd/common/gfx9: workaround DCC corruption more conservatively

Fixes KHR-GL45.texture_swizzle.smoke and others on Vega.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102809


Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit f9ccfda9)