commit 0f57e168 upstream.

Currently, pch_spi_start_transfer failure is not anticipated.
This patch adds the processing.
Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>