IB/mlx4: Fix an error handling path in 'mlx4_ib_rereg_user_mr()'

Before returning -EPERM we should release some resources, as already done
in the other error handling path of the function.

Fixes: d8f9cc32 ("IB/mlx4: Mark user MR as writable if actual virtual memory is writable")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>