spi: Fix htmldocs build error due struct spi_replaced_transfers

The kernel-doc has to be just before the structure definition but the one
for struct spi_replaced_transfers was before a structure declaration and
that confuses kernel-doc which complains with the following build error:

.//include/linux/spi/spi.h:933: error: Cannot parse struct or union!
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi.h

@@ -898,6 +898,10 @@ spi_max_transfer_size(struct spi_device *spi)
 
 /* SPI transfer replacement methods which make use of spi_res */
 
+struct spi_replaced_transfers;
+typedef void (*spi_replaced_release_t)(struct spi_master *master,
+				       struct spi_message *msg,
+				       struct spi_replaced_transfers *res);
 /**
  * struct spi_replaced_transfers - structure describing the spi_transfer
  *                                 replacements that have occurred
@@ -917,10 +921,6 @@ spi_max_transfer_size(struct spi_device *spi)
  * if some extra allocation is requested, so alignment will be the same
  * as for spi_transfers
  */
-struct spi_replaced_transfers;
-typedef void (*spi_replaced_release_t)(struct spi_master *master,
-				       struct spi_message *msg,
-				       struct spi_replaced_transfers *res);
 struct spi_replaced_transfers {
 	spi_replaced_release_t release;
 	void *extradata;