commoncap: move assignment of fs_ns to avoid null pointer dereference

commoncap: move assignment of fs_ns to avoid null pointer dereference

The pointer fs_ns is assigned from inode->i_ib->s_user_ns before
a null pointer check on inode, hence if inode is actually null we
will get a null pointer dereference on this assignment. Fix this
by only dereferencing inode after the null pointer check on
inode.

Detected by CoverityScan CID#1455328 ("Dereference before null check")

Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities")
Signed-off-by: Colin Ian King <[email protected]>
Cc: [email protected]
Acked-by: Serge Hallyn <[email protected]>
Signed-off-by: James Morris <[email protected]>