p54spi: always call p54spi_sleep in p54spi_tx_frame if p54spi_wakeup succeeded

Put chip into sleep state, once it's been awaken.
Also, propagate error code to the caller.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>