sb/intel/i82801jx/Makefile.inc: Remove path to non-existent folder

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

Change-Id: I2e69822575e42b322eb971540821f3b87fb7e903
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70384
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>

src/southbridge/intel/i82801jx/Makefile.inc

@@ -21,6 +21,4 @@ ramstage-y += ../common/pciehp.c
 
 smm-y += smihandler.c
 
-CPPFLAGS_common += -I$(src)/southbridge/intel/i82801jx/include
-
 endif