fix the fsid_t structure to match name of __val

this is a case of poorly written man pages not matching the actual
implementation, and why i hate implementing nonstandard interfaces
with no actual documentation of how they're intended to work.

include/sys/statfs.h

@@ -4,7 +4,7 @@
 #include <sys/statvfs.h>
 
 typedef struct {
-	int val[2];
+	int __val[2];
 } fsid_t;
 
 #include <bits/statfs.h>