iwlwifi: mvm: trim sched scan delay down to 16-bit for LMAC as well

In theory, LMAC scans can handle a 32-bit delay, but since waiting for
over 18 hours to start the scan is a bit silly and to keep it aligned
with UMAC scans (which only support 16-bit delays), trim it down to
16-bits.

This makes the LMAC vs. UMAC and the UMAC reg scan vs. UMAC sched scan
code more similar.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>