platform/mellanox: mlxreg-lc: fix error code in mlxreg_lc_create_static_devices()

This code should be using PTR_ERR() instead of IS_ERR().  And because
it's using the wrong "dev->client" pointer, the IS_ERR() check will be
false, meaning the function returns success.

Fixes: 62f9529b ("platform/mellanox: mlxreg-lc: Add initial support for Nvidia line card devices")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20211110074346.GB5176@kili


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>