programmer: Smoothen register_spi_master() API

It was impossible to register a const struct spi_master that would
point to dynamically allocated `data`. Fix that so that we won't
have to create more mutable globals.

Change-Id: I0c753b3db050fb87d4bbe2301a7ead854f28456f
Signed-off-by: Nico Huber <nico.h@gmx.de>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/54066
Original-Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72179
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/pickit2_spi.c b/pickit2_spi.c
index 9c78138..5d0b573 100644
--- a/pickit2_spi.c
+++ b/pickit2_spi.c
@@ -500,7 +500,7 @@
 
 	if (register_shutdown(pickit2_shutdown, pickit2_data))
 		goto init_err_cleanup_exit;
-	register_spi_master(&spi_master_pickit2);
+	register_spi_master(&spi_master_pickit2, NULL);
 
 	return 0;