drm: Check polling initialized before enabling in drm_helper_probe_single_connector_modes

drm: Check polling initialized before enabling in drm_helper_probe_single_connector_modes

In function drm_helper_probe_single_connector_modes() when we enable
polling again, if it is already uninitialized, a warning is reported.
This patch fixes the warning message by checking if poll is initialized
before enabling it.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202401191128.db8423f1-oliver.sang@intel.com
Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1706856224-9725-1-git-send-email-shradhagupta@linux.microsoft.com