spi/spi_sh: use spi_unregister_master instead of spi_master_put in remove path

spi_master_put() should only be used in error handling.
Once spi_register_master() returns success, we should call
spi_unregister_master() instead.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>