mb/google/kahlee/var/careena: Make sure bid isn't used uninitialized

GCC with LTO cought this.

Warning:
src/mainboard/google/kahlee/variants/careena/variant.c:44:12: error: 'bid' may be used uninitialized [-Werror=maybe-uninitialized]
   44 |         if (bid == 7)
      |            ^
src/mainboard/google/kahlee/variants/careena/variant.c: In function 'car_stage_entry':
src/mainboard/google/kahlee/variants/careena/variant.c:24:18: note: 'bid' was declared here
   24 |         uint32_t bid;

Change-Id: Ie732b5be5cd9dc0abaf1a5efe023bcb0738dba1d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84206
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-by: coreboot org <coreboot.org@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/kahlee/variants/careena/variant.c

@@ -38,7 +38,8 @@ void variant_romstage_entry(void)
 		}
 	}
 
-	google_chromeec_get_board_version(&bid);
+	if (google_chromeec_get_board_version(&bid))
+		return;
 
 	if (bid == 7)
 		/*