spi: Fixes for v4.9 A few small fixes for SPI, one core fix that only applies in cases where we're handling DT overlays and a couple of driver specific fixes: - Fix handling of error cases when instantiating DT overlays so we don't end up just ignoring devices that encountered an error during instantiation. - Avoid reading uninitialized data when handing spurious interrupts in the espi driver. - A driver specific fix for the dspi driver to fix a bad interaction with u-boot.