Instead of using asynchronous SPI API and then spinning waiting for SPI
transfer to complete when disabling the device, let's use threaded IRQ
model and spi_sync().
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Tested-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>