bitbang: Make use of new register_spi_master() API

BUG=b:185191942
TEST=builds

Change-Id: I8f251910cec728a78b79c17de355bcf0c736c69a
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/55087
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
diff --git a/bitbang_spi.c b/bitbang_spi.c
index 85c867e..e70d883 100644
--- a/bitbang_spi.c
+++ b/bitbang_spi.c
@@ -161,8 +161,7 @@
 
 	struct bitbang_spi_master_data *data = calloc(1, sizeof(struct bitbang_spi_master_data));
 	data->master = master;
-	mst.data = data;
-	register_spi_master(&mst, NULL);
+	register_spi_master(&mst, data);
 	register_shutdown(bitbang_spi_shutdown, data);
 
 	/* Only mess with the bus if we're sure nobody else uses it. */