wifi: brcmfmac: make per-vendor event map const

The event map is not intended to change so make it const.

Tested-by: James Prestwood <prestwoj@gmail.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://patch.msgid.link/20250425085519.492267-3-arend.vanspriel@broadcom.com


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