Currently the DebugFS logic in utils/fwlog/dbglog_host.c is protected
by the flag WLAN_OPEN_SOURCE. The WLAN_OPEN_SOURCE flag is a legacy
flag which had a specific use that is no longer valid. So replace the
use of WLAN_OPEN_SOURCE with a feature-specific flag.
Change-Id: I82c51efff8dfe6673c6b9d956f974cae2d21bb69
CRs-Fixed: 3464911