drm/i915/display: Fix Panel Replay vblank enable workaround

Currently workaround is not applied when vblank is enabled on crtc that
needs the workaround if vblank is already enabled for another crtc that
doesn't need the workaround. Fix this by increasing counter only if crtc
needs the workaround.

Fixes: aa451abc ("drm/i915/display: Prevent DC6 while vblank is enabled for Panel Replay")
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241009134225.1322820-2-jouni.hogander@intel.com