spi: Fix crash with double message finalisation on error handling

This reverts commit e120cc0d.

It causes a NULL pointer dereference with drivers using the generic
spi_transfer_one_message(), which always calls
spi_finalize_current_message(), which zeroes master->cur_msg.

Drivers implementing transfer_one_message() theirselves must always call
spi_finalize_current_message(), even if the transfer failed:

 * @transfer_one_message: the subsystem calls the driver to transfer a single
 *      message while queuing transfers that arrive in the meantime. When the
 *      driver is finished with this message, it must call
 *      spi_finalize_current_message() so the subsystem can issue the next
 *      transfer

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@linaro.org>