drm/amd/display: Check null pointer before dereferencing se

BugLink: https://bugs.launchpad.net/bugs/2097301

[ Upstream commit ff599ef ]

[WHAT & HOW]
se is null checked previously in the same function, indicating
it might be null; therefore, it must be checked when used again.

This fixes 1 FORWARD_NULL issue reported by Coverity.

Acked-by: Alex Hung <[email protected]>
Reviewed-by: Rodrigo Siqueira <[email protected]>
Signed-off-by: Alex Hung <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
CVE-2024-50049
Signed-off-by: Manuel Diewald <[email protected]>
Signed-off-by: Koichiro Den <[email protected]>

Author: Alex Hung

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -1786,7 +1786,7 @@ bool dc_validate_boot_timing(const struct dc *dc,
 		if (crtc_timing->pix_clk_100hz != pix_clk_100hz)
 			return false;
 
-		if (!se->funcs->dp_get_pixel_format)
+		if (!se || !se->funcs->dp_get_pixel_format)
 			return false;
 
 		if (!se->funcs->dp_get_pixel_format(