spi: core: Fix spi_register_master error handling

In the case spi_master_initialize_queue() fails, current code calls
device_unregister() before return error from spi_register_master().
However, all the drivers call spi_master_put() in the error path if
spi_register_master() fails. Thus we should call device_del() rather than
device_unregister() before return error from spi_register_master().

This also makes all the spi_register_master() error handling consistent,
because all other error paths of spi_register_master() expect drivers to
call spi_master_put() if spi_register_master() fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>