buspirate_spi: Fix a missing error check during _init()

Change-Id: I17c6737853bf311b3f7aa9bfb10b54ce19e95ecc
Signed-off-by: Richard Hughes <richard@hughsie.com>
Reviewed-on: https://review.coreboot.org/c/30407
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
1 file changed