drm/amdgpu: properly handle vbios fake edid sizing

The comment in the vbios structure says:
// = 128 means EDID length is 128 bytes, otherwise the EDID length = ucFakeEDIDLength*128

This fake edid struct has not been used in a long time, so I'm
not sure if there were actually any boards out there with a non-128 byte
EDID, but align the code with the comment.
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Reported-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lists.freedesktop.org/archives/amd-gfx/2024-June/109964.html
Fixes: d38ceaf9 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/atombios_encoders.c

@@ -2065,26 +2065,29 @@ amdgpu_atombios_encoder_get_lcd_info(struct amdgpu_encoder *encoder)
 					fake_edid_record = (ATOM_FAKE_EDID_PATCH_RECORD *)record;
 					if (fake_edid_record->ucFakeEDIDLength) {
 						struct edid *edid;
-						int edid_size =
-							max((int)EDID_LENGTH, (int)fake_edid_record->ucFakeEDIDLength);
-						edid = kmalloc(edid_size, GFP_KERNEL);
-						if (edid) {
-							memcpy((u8 *)edid, (u8 *)&fake_edid_record->ucFakeEDIDString[0],
-							       fake_edid_record->ucFakeEDIDLength);
+						int edid_size;
 
+						if (fake_edid_record->ucFakeEDIDLength == 128)
+							edid_size = fake_edid_record->ucFakeEDIDLength;
+						else
+							edid_size = fake_edid_record->ucFakeEDIDLength * 128;
+						edid = kmemdup(&fake_edid_record->ucFakeEDIDString[0],
+							       edid_size, GFP_KERNEL);
+						if (edid) {
 							if (drm_edid_is_valid(edid)) {
 								adev->mode_info.bios_hardcoded_edid = edid;
 								adev->mode_info.bios_hardcoded_edid_size = edid_size;
-							} else
+							} else {
 								kfree(edid);
 							}
 						}
-					record += fake_edid_record->ucFakeEDIDLength ?
-						  struct_size(fake_edid_record,
+						record += struct_size(fake_edid_record,
 								      ucFakeEDIDString,
-							      fake_edid_record->ucFakeEDIDLength) :
+								      edid_size);
+					} else {
 						/* empty fake edid record must be 3 bytes long */
-						  sizeof(ATOM_FAKE_EDID_PATCH_RECORD) + 1;
+						record += sizeof(ATOM_FAKE_EDID_PATCH_RECORD) + 1;
+					}
 					break;
 				case LCD_PANEL_RESOLUTION_RECORD_TYPE:
 					panel_res_record = (ATOM_PANEL_RESOLUTION_PATCH_RECORD *)record;