payloads/tianocore: Add missing CONFIG for SERIAL_SUPPORT

This caused edk2 serial output to be disabled 100% of the time.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: If272369b405e7745fe82f49026cbed0abc50f355
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66160
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
diff --git a/payloads/external/Makefile.inc b/payloads/external/Makefile.inc
index 3749b9e..0225e50 100644
--- a/payloads/external/Makefile.inc
+++ b/payloads/external/Makefile.inc
@@ -176,7 +176,7 @@
 		CONFIG_TIANOCORE_HAVE_EFI_SHELL=$(CONFIG_TIANOCORE_HAVE_EFI_SHELL) \
 		CONFIG_TIANOCORE_PRIORITIZE_INTERNAL=$(CONFIG_TIANOCORE_PRIORITIZE_INTERNAL) \
 		CONFIG_TIANOCORE_PS2_SUPPORT=$(CONFIG_TIANOCORE_PS2_SUPPORT) \
-		CONFIG_TIANOCORE_SERIAL_SUPPORT=$(TIANOCORE_SERIAL_SUPPORT) \
+		CONFIG_TIANOCORE_SERIAL_SUPPORT=$(CONFIG_TIANOCORE_SERIAL_SUPPORT) \
 		CONFIG_TIANOCORE_SD_MMC_TIMEOUT=$(CONFIG_TIANOCORE_SD_MMC_TIMEOUT) \
 		CONFIG_TIANOCORE_USE_8254_TIMER=$(CONFIG_TIANOCORE_USE_8254_TIMER) \
 		CONFIG_ECAM_MMCONF_BASE_ADDRESS=$(CONFIG_ECAM_MMCONF_BASE_ADDRESS) \