wwan: core: Unshadow error code returned by ida_alloc_range()

ida_alloc_range() may return other than -ENOMEM error code.
Unshadow it in the wwan_create_port().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>