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/wbsio_spi.c b/wbsio_spi.c
index 9145814..d7c1b0b 100644
--- a/wbsio_spi.c
+++ b/wbsio_spi.c
@@ -85,7 +85,7 @@
 	msg_pdbg("%s: Winbond saved on 4 register bits so max chip size is "
 		 "1024 kB!\n", __func__);
 	max_rom_decode.spi = 1024 * 1024;
-	register_spi_master(&spi_master_wbsio);
+	register_spi_master(&spi_master_wbsio, NULL);
 
 	return 0;
 }