tests: fix update-exp: soft_uart_test overwrites rlp_test.ok

Change-Id: I41ea2c3d5b1e2e0349740acd63c39413472e0dad
Fixes: 9ef304dd2 "soft_uart: add unit tests for the receiver and transmitter"
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 4eac635..72ecc1e 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -709,7 +709,7 @@
 		>$(srcdir)/osmo_io/osmo_io_test.ok \
 		2>$(srcdir)/osmo_io/osmo_io_test.err
 	soft_uart/soft_uart_test \
-		>$(srcdir)/soft_uart/soft_uart.ok \
+		>$(srcdir)/soft_uart/soft_uart.ok
 	rlp/rlp_test \
 		>$(srcdir)/rlp/rlp_test.ok \
 	$(NULL)