i.group: use standardized option from subgroups

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@57705 15284696-431f-4ddb-bdfa-cd5b030d7da7

imagery/i.group/main.c

@@ -58,11 +58,9 @@ int main(int argc, char *argv[])
     grp = G_define_standard_option(G_OPT_I_GROUP);
     grp->description = _("Name of imagery group");
 
-    sgrp = G_define_option();
-    sgrp->key = "subgroup";
-    sgrp->type = TYPE_STRING;
+    sgrp = G_define_standard_option(G_OPT_I_SUBGROUP);
     sgrp->required = NO;
-    sgrp->description = _("Name of imagery sub-group");
+    sgrp->description = _("Name of imagery subgroup");
 
     rast = G_define_standard_option(G_OPT_R_INPUTS);
     rast->required = NO;	/* -l flag */