drm/i915/display: Add warn_on in intel_psr_pause()

drm/i915/display: Add warn_on in intel_psr_pause()

Right now the only user of psr_pause/resume is intel_cdclk but
additional users will be added in the future and we may need
do reference counting for PSR pause and resume, for now only adding a
warn_on so this cases do not go unnoticed.

Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Jouni Hogander <jouni.hogander@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211020003558.222198-2-jose.souza@intel.com