drm/i915/ringbuffer: Only print an error on the second attempt to reset head

There's not much we can do here but hope for the best. However the first
failure happens quite frequently and if often remedied by the second
attempt to reset HEAD. So only print the error if that attempt also
fails.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=19802
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org