spi: correct the transfer_one_message documentation wording

The transfer_one_message callback handles messages, not transfers.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index ad050f0..4203c66 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -273,7 +273,7 @@
  *	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
+ *	message
  * @unprepare_transfer_hardware: there are currently no more messages on the
  *	queue so the subsystem notifies the driver that it may relax the
  *	hardware by issuing this call