spi: make xmldocs warning caused by spi.c

This patch fix following warnings while make xmldocs.

.//drivers/spi/spi.c:2354: warning: Excess function parameter
'message' description in 'spi_split_transfers_maxsize'
.//drivers/spi/spi.c:2354: warning: Excess function parameter
 'max_size' description in 'spi_split_transfers_maxsize'

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>