drm/amd/display: Fix Coverity INTEGER_OVERFLOW within decide_fallback_link_setting_max_bw_policy

[Why]
For addtion (uint8_t) variable + constant 1,
coverity generates message below:
Truncation due to cast operation on "cur_idx + 1" from
32 to 8 bits.

Then Coverity assume result is 32 bits value be saved into
8 bits variable. When result is used as index to access
array, Coverity suspects index invalid.

[How]
Change varaible type to uint32_t.
Reviewed-by: Alex Hung <alex.hung@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -534,7 +534,7 @@ static bool decide_fallback_link_setting_max_bw_policy(
 		struct dc_link_settings *cur,
 		enum link_training_result training_result)
 {
-	uint8_t cur_idx = 0, next_idx;
+	uint32_t cur_idx = 0, next_idx;
 	bool found = false;
 
 	if (training_result == LINK_TRAINING_ABORT)