patch 9.0.0398: members of funccall_T are inconsistently named

Problem:    Members of funccall_T are inconsistently named.
Solution:   Use the "fc_" prefix for all members.
diff --git a/src/evalvars.c b/src/evalvars.c
index 0d1fe82..facafc7 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -3391,7 +3391,8 @@
     if (*name == 'v')				// v: variable
 	return &vimvarht;
     if (get_current_funccal() != NULL
-	       && get_current_funccal()->func->uf_def_status == UF_NOT_COMPILED)
+	       && get_current_funccal()->fc_func->uf_def_status
+							    == UF_NOT_COMPILED)
     {
 	// a: and l: are only used in functions defined with ":function"
 	if (*name == 'a')			// a: function argument