drm/radeon/kms: fix RADEON_INFO_CRTC_FROM_ID info ioctl

Return the crtc_id, not the counter value.  They are not
necessarily the same.

Cc: Jerome Glisse <glisse@freedesktop.org>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>