DB_COMMAND(9): correct mdoc markup for .Nm entries

Add missing commas after .Nm entries.

MFC after:	1 week
Reported by:	make manlint

share/man/man9/DB_COMMAND.9

@@ -40,9 +40,9 @@
 .Nm DB_SHOW_ALIAS_FLAGS ,
 .Nm DB_SHOW_ALL_ALIAS ,
 .Nm DB_TABLE_ALIAS ,
-.Nm DB_TABLE_ALIAS_FLAGS
+.Nm DB_TABLE_ALIAS_FLAGS ,
 .Nm DB_DECLARE_TABLE ,
-.Nm DB_DEFINE_TABLE ,
+.Nm DB_DEFINE_TABLE
 .Nd Extends the ddb command set
 .Sh SYNOPSIS
 .In ddb/ddb.h