vc/eltan/security/mboot/Makefile.inc: Remove path to non-existent folder

Found using 'Wmissing-include-dirs' command option.

Change-Id: Ie2c4a6c2bb55af56cb6e0b013b1a2ed9baa787ef
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70460
Reviewed-by: Erik van den Bogaert <ebogaert@eltan.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/vendorcode/eltan/security/mboot/Makefile.inc b/src/vendorcode/eltan/security/mboot/Makefile.inc
index 22729af..99db2c3 100644
--- a/src/vendorcode/eltan/security/mboot/Makefile.inc
+++ b/src/vendorcode/eltan/security/mboot/Makefile.inc
@@ -1,9 +1,5 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
-ifneq ($(filter y,$(CONFIG_VENDORCODE_ELTAN_VBOOT) $(CONFIG_VENDORCODE_ELTAN_MBOOT)),)
-CPPFLAGS_common += -I$(src)/security/mboot
-endif
-
 ifeq ($(CONFIG_VENDORCODE_ELTAN_MBOOT),y)
 postcar-y += mboot.c