ext4: use kmem_cache_zalloc() in ext4_init_io_end()

Use advantage of kmem_cache_zalloc() to remove a memset() call in
ext4_init_io_end() and save a few bytes.

Before:
 [jj@dragon linux-2.6]$ size fs/ext4/page-io.o
    text    data     bss     dec     hex filename
    3016       0     624    3640     e38 fs/ext4/page-io.o
After:
 [jj@dragon linux-2.6]$ size fs/ext4/page-io.o
    text    data     bss     dec     hex filename
    3000       0     624    3624     e28 fs/ext4/page-io.o
Signed-off-by: NJesper Juhl <jj@chaosbits.net>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/page-io.c

@@ -158,11 +158,8 @@ static void ext4_end_io_work(struct work_struct *work)
 
 ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
 {
-	ext4_io_end_t *io = NULL;
-
-	io = kmem_cache_alloc(io_end_cachep, flags);
+	ext4_io_end_t *io = kmem_cache_zalloc(io_end_cachep, flags);
 	if (io) {
-		memset(io, 0, sizeof(*io));
 		atomic_inc(&EXT4_I(inode)->i_ioend_count);
 		io->inode = inode;
 		INIT_WORK(&io->work, ext4_end_io_work);