drm/amd/display: Add NULL check for clk_mgr and clk_mgr->funcs in dcn30_init_hw

This commit addresses a potential null pointer dereference issue in the
`dcn30_init_hw` function. The issue could occur when `dc->clk_mgr` or
`dc->clk_mgr->funcs` is null.

The fix adds a check to ensure `dc->clk_mgr` and `dc->clk_mgr->funcs` is
not null before accessing its functions. This prevents a potential null
pointer dereference.

Reported by smatch:
drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn30/dcn30_hwseq.c:789 dcn30_init_hw() error: we previously assumed 'dc->clk_mgr' could be null (see line 628)

Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn30/dcn30_hwseq.c

@@ -625,7 +625,7 @@ void dcn30_init_hw(struct dc *dc)
 	uint32_t backlight = MAX_BACKLIGHT_LEVEL;
 	uint32_t user_level = MAX_BACKLIGHT_LEVEL;
 
-	if (dc->clk_mgr && dc->clk_mgr->funcs->init_clocks)
+	if (dc->clk_mgr && dc->clk_mgr->funcs && dc->clk_mgr->funcs->init_clocks)
 		dc->clk_mgr->funcs->init_clocks(dc->clk_mgr);
 
 	// Initialize the dccg
@@ -786,11 +786,12 @@ void dcn30_init_hw(struct dc *dc)
 	if (!dcb->funcs->is_accelerated_mode(dcb) && dc->res_pool->hubbub->funcs->init_watermarks)
 		dc->res_pool->hubbub->funcs->init_watermarks(dc->res_pool->hubbub);
 
-	if (dc->clk_mgr->funcs->notify_wm_ranges)
+	if (dc->clk_mgr && dc->clk_mgr->funcs && dc->clk_mgr->funcs->notify_wm_ranges)
 		dc->clk_mgr->funcs->notify_wm_ranges(dc->clk_mgr);
 
 	//if softmax is enabled then hardmax will be set by a different call
-	if (dc->clk_mgr->funcs->set_hard_max_memclk && !dc->clk_mgr->dc_mode_softmax_enabled)
+	if (dc->clk_mgr && dc->clk_mgr->funcs && dc->clk_mgr->funcs->set_hard_max_memclk &&
+	    !dc->clk_mgr->dc_mode_softmax_enabled)
 		dc->clk_mgr->funcs->set_hard_max_memclk(dc->clk_mgr);
 
 	if (dc->res_pool->hubbub->funcs->force_pstate_change_control)