efi/libstub: gop: Fix EDID support in mixed-mode

The efi_edid_discovered_protocol and efi_edid_active_protocol have mixed
mode fields. So all their attributes should be accessed through
the efi_table_attr() helper.

Doing so fixes the upper 32 bits of the 64 bit gop_edid pointer getting
set to random values (followed by a crash at boot) when booting a x86_64
kernel on a machine with 32 bit UEFI like the Asus T100TA.

Fixes: 17029cdd8f9d ("efi/libstub: gop: Add support for reading EDID")
Cc: Thomas Zimmermann <[e-mail]>
Cc: Javier Martinez Canillas <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>

drivers/firmware/efi/libstub/gop.c

···
 		status = efi_bs_call(handle_protocol, handle, &EFI_EDID_ACTIVE_PROTOCOL_GUID,
 				     (void **)&active_edid);
 		if (status == EFI_SUCCESS) {
-			gop_size_of_edid = active_edid->size_of_edid;
-			gop_edid = active_edid->edid;
+			gop_size_of_edid = efi_table_attr(active_edid, size_of_edid);
+			gop_edid = efi_table_attr(active_edid, edid);
 		} else {
 			status = efi_bs_call(handle_protocol, handle,
 					     &EFI_EDID_DISCOVERED_PROTOCOL_GUID,
 					     (void **)&discovered_edid);
 			if (status == EFI_SUCCESS) {
-				gop_size_of_edid = discovered_edid->size_of_edid;
-				gop_edid = discovered_edid->edid;
+				gop_size_of_edid = efi_table_attr(discovered_edid, size_of_edid);
+				gop_edid = efi_table_attr(discovered_edid, edid);
 			}
 		}