BUG-1630: fix warning message format

The bug has been reasolved by change
I4a35ff27725dab7f35b83ae1bcc6d728a313bd1c, this patch just fixes the
message format.

Change-Id: Ic77f0675c8adb1c6d2ba29ea555335e7eaba4a34
Signed-off-by: Robert Varga <rovarga@cisco.com>