drm/hdcp: drm_hdcp_request_srm() as static

Below Sparsh warnings are fixed.

Commit: drm: revocation check at drm subsystem
+drivers/gpu/drm/drm_hdcp.c:235:6: warning: symbol
'drm_hdcp_request_srm' was not declared. Should it be static?
+drivers/gpu/drm/drm_hdcp.c:27:3: warning: symbol 'srm_data' was not
declared. Should it be static?
+drivers/gpu/drm/drm_hdcp.c:317:5: warning: symbol 'drm_setup_hdcp_srm'
was not declared. Should it be static?
+drivers/gpu/drm/drm_hdcp.c:327:6: warning: symbol
'drm_teardown_hdcp_srm' was not declared. Should it be static?

cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190513133504.18612-1-ramalingam.c@intel.com