FmpDevicePkg/FmpDxe: Better warn of potential ImageTypeId misconfig

FmpDevicePkg/FmpDxe: Better warn of potential ImageTypeId misconfig

A user may fall through to the case they depend on the
PcdFmpDeviceImageTypeIdGuid value to get the ImageTypeId GUID
value. The default PCD value is 0 (NULL) so the code would
further fall back on the gEfiCallerIdGuid value.

This change modifies the print error level for the message that
indicates this occurred to DEBUG_WARN from DEBUG_INFO to better
warn the user that this occurred.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Guomin Jiang <guomin.jiang@intel.com>
Cc: Wei6 Xu <wei6.xu@intel.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Guomin Jiang <guomin.jiang@intel.com>
Reviewed-by: Wei6 Xu <wei6.xu@intel.com>