spi_master: Use new API to register shutdown function

This allows spi masters to register shutdown function in spi_master
struct, which means there is no need to call register_shutdown in init
function, since this call is now a part of register_spi_master.

As a consequence of using new API, two things are happening here:
1) No resource leakage anymore in case register_shutdown() would fail,
2) Fixed propagation of register_spi_master() return values.

Basic testing: when I comment out free(data) in linux_spi_shutdown, test
fails with error
../linux_spi.c:235: note: block 0x55a4db276510 allocated here
ERROR: linux_spi_init_and_shutdown_test_success leaked 1 block(s)
Means, shutdown function is invoked.

BUG=b:185191942
TEST= 1) builds and ninja test including CB:56911
2) On ARMv7 device
flashrom -p linux_spi -V
-> using linux_spi, chip found
3) On x86_64 AMD device
flashrom -p internal -V
-> this is actually using sb600spi, chip found

Change-Id: Ib60300f9ddb295a255d5ef3f8da0e07064207140
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/56103
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>

realtek_mst_i2c_spi.c

@@ -440,6 +440,7 @@ static const struct spi_master spi_master_i2c_realtek_mst = {
 	.read = realtek_mst_i2c_spi_read,
 	.write_256 = realtek_mst_i2c_spi_write_256,
 	.write_aai = realtek_mst_i2c_spi_write_aai,
+	.shutdown = realtek_mst_i2c_spi_shutdown,
 };
 
 static int get_params(int *reset, int *enter_isp)
@@ -512,10 +513,7 @@ static int realtek_mst_i2c_spi_init(void)
 
 	data->fd = fd;
 	data->reset = reset;
-	ret |= register_shutdown(realtek_mst_i2c_spi_shutdown, data);
-	ret |= register_spi_master(&spi_master_i2c_realtek_mst, data);
-
-	return ret;
+	return register_spi_master(&spi_master_i2c_realtek_mst, data);
 }
 
 const struct programmer_entry programmer_realtek_mst_i2c_spi = {