util/lint/lint-stable-019: Update grep '\s' to [[:blank:]]

For some reason, the '\s' syntax is causing an error for me under
freebsd.  It's entirely possible that I'm doing something wrong, but
this change should be fine regardless.

Freebsd's grep, GNU grep, and git grep all handle posix regex classes,
so this change should be transparent.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I489ec13b4ea2e9c17692888e42b8741763b1a2c5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63532
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>

util/lint/lint-stable-019-header-files

@@ -22,7 +22,7 @@ else
 fi
 
 for header in $HEADER_FILES; do
-	${GREP_FILES} "#\s*include\s\+[\"<]\s*${header}\.h\s*[\">]" | \
+	${GREP_FILES} "#[[:blank:]]*include[[:blank:]]\+[\"<][[:blank:]]*${header}\.h[[:blank:]]*[\">]" | \
 		grep "$INCLUDED_DIRS" | \
 		grep -v "$EXCLUDED_FILES"; \
 done