IB/mlx5: Use 'kvfree()' for memory allocated by 'kvzalloc()'

When 'kvzalloc()' is used to allocate memory, 'kvfree()' must be used to
free it.

Fixes: 1cbe6fc8

 ("IB/mlx5: Add support for CQE compressing")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>