drm/radeon: fix card_posted check for newer asics

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>
Cc: stable@vger.kernel.org