drm/i915: do not mix workaround with normal flow

Separate the two comments: one is a workaround and the other is a sanity
check. We could just compare != 1, but let's treat them differently due
to having different meaning.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190404230426.15837-4-lucas.demarchi@intel.com