commit 09fb8bd1 upstream.

Newer asics have variable numbers of crtcs.  Use that
rather than the asic family to determine which crtcs
to check.  This avoids checking non-existent crtcs or
missing crtcs on certain asics.
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>