spi25_statusreg: Return defined value on failed RDSR

The interface of spi_read_status_register() is broken and can't return
errors. Let's not return random stack data at least.

Change-Id: I714b20001a5443bba665c2e0061ca14069777581
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/22017
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
(cherry picked from commit 1f081530b60ee805532f106f59cc33973e160481)
Reviewed-on: https://review.coreboot.org/22349
1 file changed