vfs: clear to the end of the buffer on partial buffer reads

READ is zero so the "rw & READ" test is always false.  The intended test
was "((rw & RW_MASK) == READ)".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/buffer.c

@@ -2935,7 +2935,7 @@ static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
 	bio->bi_io_vec[0].bv_len = bytes;
 
 	/* ..and clear the end of the buffer for reads */
-	if (rw & READ) {
+	if ((rw & RW_MASK) == READ) {
 		void *kaddr = kmap_atomic(bh->b_page);
 		memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
 		kunmap_atomic(kaddr);