iwlwifi: pcie: returning positive instead of negative

There is a missing '-' character here so we return positive 'ENOMEM'
instead of negative.  The caller doesn't care.  All non-zero returns
are translated to '-ENOMEM' in iwl_pcie_nic_init().

This is just a cleanup.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>