drm/amd/display: Add 'replay' NULL check in 'edp_set_replay_allow_active()'

In the first if statement, we're checking if 'replay' is NULL. But in
the second if statement, we're not checking if 'replay' is NULL again
before calling replay->funcs->replay_set_power_opt().

if (replay == NULL && force_static)
    return false;

...

if (link->replay_settings.replay_feature_enabled &&
    replay->funcs->replay_set_power_opt) {
	replay->funcs->replay_set_power_opt(replay, *power_opts, panel_inst);
	link->replay_settings.replay_power_opt_active = *power_opts;
}

If 'replay' is NULL, this will cause a null pointer dereference.

Fixes the below found by smatch:
drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_edp_panel_control.c:895 edp_set_replay_allow_active() error: we previously assumed 'replay' could be null (see line 887)

Fixes: c7ddc0a ("drm/amd/display: Add Functions to enable Freesync Panel Replay")
Cc: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Suggested-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: srishanm

drivers/gpu/drm/amd/display/dc/link/protocols/link_edp_panel_control.c

@@ -892,7 +892,8 @@ bool edp_set_replay_allow_active(struct dc_link *link, const bool *allow_active,
 
 	/* Set power optimization flag */
 	if (power_opts && link->replay_settings.replay_power_opt_active != *power_opts) {
-		if (link->replay_settings.replay_feature_enabled && replay->funcs->replay_set_power_opt) {
+		if (replay != NULL && link->replay_settings.replay_feature_enabled &&
+		    replay->funcs->replay_set_power_opt) {
 			replay->funcs->replay_set_power_opt(replay, *power_opts, panel_inst);
 			link->replay_settings.replay_power_opt_active = *power_opts;
 		}