patch 8.0.0897: wrong error message for invalid term_finish value

Problem:    Wrong error message for invalid term_finish value
Solution:   Pass the right argument to emsg().
diff --git a/src/channel.c b/src/channel.c
index 4e1458c..19d3c5d 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -4426,7 +4426,7 @@
 		val = get_tv_string(item);
 		if (STRCMP(val, "open") != 0 && STRCMP(val, "close") != 0)
 		{
-		    EMSG2(_(e_invarg2), "drop");
+		    EMSG2(_(e_invarg2), val);
 		    return FAIL;
 		}
 		opt->jo_set2 |= JO2_TERM_FINISH;