drm/i915: Don't warn if the workaround list is empty part 2.

Extend the same reasoning as in the patch listed below.  It's not an
error for the workaround list to be empty if no workarounds are needed.

    commit 02235808
    Author: Francisco Jerez <currojerez@riseup.net>
    Date:   Wed Oct 7 14:44:01 2015 +0300
        drm/i915: Don't warn if the workaround list is empty.

Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452129330-3484-2-git-send-email-rodrigo.vivi@intel.com