kbuild: fix trivial typo in comment

Add missing underscore in CONFIG_DEBUG_INFO_BTF_MODULES.

Fixes: f73edc89 ("kbuild: unify two modpost invocations")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1538,7 +1538,7 @@ endif
 # Build modules
 #
 
-# *.ko are usually independent of vmlinux, but CONFIG_DEBUG_INFOBTF_MODULES
+# *.ko are usually independent of vmlinux, but CONFIG_DEBUG_INFO_BTF_MODULES
 # is an exception.
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 KBUILD_BUILTIN := 1