aco: fix printing assembly with CLRXdisasm on GFX6

aco: fix printing assembly with CLRXdisasm on GFX6

We thought that CLRXdisasm allowed gfx600 as well as gfx700 but
it actually doesn't. Use the family for GFX6 chips instead.

Fixes: 0099f85232b ("aco: print assembly with CLRXdisasm for GFX6-GFX7 if found on the system")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3531>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3531>