fix statfs struct on mips

The mips statfs struct layout is different than on other archs, so the
statfs, fstatfs, statvfs and fstatvfs APIs were broken on mips.
Now the ordering is fixed, the types are kept consistent with other archs.

arch/mips/bits/statfs.h

 struct statfs {
-	unsigned long f_type, f_bsize;
-	fsblkcnt_t f_blocks, f_bfree, f_bavail;
+	unsigned long f_type, f_bsize, f_frsize;
+	fsblkcnt_t f_blocks, f_bfree;
 	fsfilcnt_t f_files, f_ffree;
+	fsblkcnt_t f_bavail;
 	fsid_t f_fsid;
-	unsigned long f_namelen, f_frsize, f_flags, f_spare[4];
+	unsigned long f_namelen, f_flags, f_spare[5];
 };