drm/amd/display: Clear shared dmub firmware state on init

[Why]
Reset the shared dmub firmware region on dmub hw init to start with
known state.

[How]
Memset the shared region to 0 in dmub_hw_init().
Suggested-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -1207,6 +1207,9 @@ static int dm_dmub_hw_init(struct amdgpu_device *adev)
 	memset(fb_info->fb[DMUB_WINDOW_6_FW_STATE].cpu_addr, 0,
 	       fb_info->fb[DMUB_WINDOW_6_FW_STATE].size);
 
+	memset(fb_info->fb[DMUB_WINDOW_SHARED_STATE].cpu_addr, 0,
+	       fb_info->fb[DMUB_WINDOW_SHARED_STATE].size);
+
 	/* Initialize hardware. */
 	memset(&hw_params, 0, sizeof(hw_params));
 	hw_params.fb_base = adev->gmc.fb_start;