test: shrink a bit

function                                             old     new   delta
test_main                                              5     434    +429
bb_test                                              473       -    -473
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/0 up/down: 429/-473)          Total: -44 bytes
   text    data     bss     dec     hex filename
 735073    3028   14408  752509   b7b7d busybox_old
 735029    3028   14408  752465   b7b51 busybox_unstripped

diff --git a/shell/ash.c b/shell/ash.c
index 35eec42..b54f666 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -10985,7 +10985,7 @@
 static int
 testcmd(int argc, char **argv)
 {
-	return bb_test(argc, argv);
+	return test_main(argc, argv);
 }
 #endif