v2: gen.c: fix the new basic test

Author: medvednikov

vlib/v2/gen/c/tests/basic_test.v vlib/v2/gen/c/tests/basictest.vvlib/v2/gen/c/tests/basic_test.v renamed to vlib/v2/gen/c/tests/basictest.v

@@ -1,6 +1,7 @@
 module main
 
 struct Point {
+mut:
 	x int
 	y int
 }