drm: bridge: cdns-mhdp8546: Fix possible null pointer dereference
In the Linux kernel, the following vulnerability has been resolved:

drm: bridge: cdns-mhdp8546: Fix possible null pointer dereference

In cdns_mhdp_atomic_enable(), the return value of drm_mode_duplicate() is
assigned to mhdp_state->current_mode, and there is a dereference of it in
drm_mode_set_name(), which will lead to a NULL pointer dereference on
failure of drm_mode_duplicate().

Fix this bug add a check of mhdp_state->current_mode.