CLEANUP: Fix typos in the h1 subsystem

Fixes typos in the code comments of the h1 subsystem.
diff --git a/include/proto/h1.h b/include/proto/h1.h
index a39cc0b..b29d76b 100644
--- a/include/proto/h1.h
+++ b/include/proto/h1.h
@@ -179,7 +179,7 @@
 	const char *ptr = b_peek(buf, start);
 	int bytes = 1;
 
-	/* NB: we'll check data availabilty at the end. It's not a
+	/* NB: we'll check data availability at the end. It's not a
 	 * problem because whatever we match first will be checked
 	 * against the correct length.
 	 */