f2fs: return success if there is no work to do

Static analysis reports this problem
file.c:3206:2: warning: Undefined or garbage value returned to caller
        return err;
        ^~~~~~~~~~

err is only set if there is some work to do.  Because the loop returns
immediately on an error, if all the work was done, a 0 would be returned.
Instead of checking the unlikely case that there was no work to do,
change the return of err to 0.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -3202,7 +3202,7 @@ int f2fs_precache_extents(struct inode *inode)
 		map.m_lblk = m_next_extent;
 	}
 
-	return err;
+	return 0;
 }
 
 static int f2fs_ioc_precache_extents(struct file *filp, unsigned long arg)