iwlwifi: mvm: fix scan request's suspend time parameter

This fix is related to a scan request when associated (bgscan).
FW expects suspend time parameter in micro seconds while the driver
provides a value in time units. This bug leads to a high traffic
latency when scan is requested while traffic is in progress.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>