jfs: Fix uninit-value access of new_ea in ea_buffer

syzbot reports that lzo1x_1_do_compress is using uninit-value:

=====================================================
BUG: KMSAN: uninit-value in lzo1x_1_do_compress+0x19f9/0x2510 lib/lzo/lzo1x_compress.c:178

...

Uninit was stored to memory at:
 ea_put fs/jfs/xattr.c:639 [inline]

...

Local variable ea_buf created at:
 __jfs_setxattr+0x5d/0x1ae0 fs/jfs/xattr.c:662
 __jfs_xattr_set+0xe6/0x1f0 fs/jfs/xattr.c:934

=====================================================

The reason is ea_buf->new_ea is not initialized properly.

Fix this by using memset to empty its content at the beginning
in ea_get().

Reported-by:  <syzbot+02341e0daa42a15ce130@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=02341e0daa42a15ce130


Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>