disp: msm: sde: fix null dereference in drm_atomic_get_property

Add changes to fix the null dereference in
drm_atomic_get_property caused by connector->state
being NULL. This change allows the drm_mode_config_reset
operation to happen before drm_dev_register to avoid this.
In current scenario, connector->state->crtc is being
accessed due to call to drm_mode_getconnector ioctl with
the drm_mode_config_reset operation pending.

Change-Id: I374d9485819fad85100d1837f4ae22fc2a3ccc40
Signed-off-by: Jayaprakash <jmadiset@codeaurora.org>