kbuild: replace $(if A,A,B) with $(or A,B) in scripts/Makefile.modpost

Similar cleanup to commit 5c816641 ("kbuild: replace $(if A,A,B)
with $(or A,B)").
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/Makefile.modpost

@@ -87,7 +87,7 @@ obj := $(KBUILD_EXTMOD)
 src := $(obj)
 
 # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
-include $(if $(wildcard $(src)/Kbuild), $(src)/Kbuild, $(src)/Makefile)
+include $(or $(wildcard $(src)/Kbuild), $(src)/Makefile)
 
 # modpost option for external modules
 MODPOST += -e