wifi: iwlwifi: return negative -EINVAL instead of positive EINVAL

The '-' character is missing in -EINVAL.

Fixes: fc7214c3 ("wifi: iwlwifi: read DSM functions from UEFI")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://msgid.link/f0391316-ab30-4664-96ac-03445ab2aeba@moroto.mountain


Signed-off-by: Johannes Berg <johannes.berg@intel.com>