fuse: do not use uninitialized i_mode

When inode is in I_NEW state, inode->i_mode is not initialized yet. Do not
use it before fuse_init_inode() is called.

Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>