f2fs: fix to update iostat correctly in f2fs_filemap_fault()

In f2fs_filemap_fault(), it fixes to update iostat info only if
VM_FAULT_LOCKED is tagged in return value of filemap_fault().

Fixes: 8b83ac8 ("f2fs: support read iostat")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/file.c

@@ -42,7 +42,7 @@ static vm_fault_t f2fs_filemap_fault(struct vm_fault *vmf)
 	vm_fault_t ret;
 
 	ret = filemap_fault(vmf);
-	if (!ret)
+	if (ret & VM_FAULT_LOCKED)
 		f2fs_update_iostat(F2FS_I_SB(inode), inode,
 					APP_MAPPED_READ_IO, F2FS_BLKSIZE);