linux_spi: Reduce maximum read chunksize

It turned out that older kernels use a single buffer of `bufsiz` bytes
for combined input and output data. So we have to account for the read
command + max 4 address bytes.

Change-Id: Ide50db38af1004fde09a70b15938e77f5e1285ac
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Tested-by: Julian von Mendel <git@jinvent.de>
Reviewed-on: https://review.coreboot.org/25149
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julian von Mendel <git@jinvent.de>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
1 file changed