spi: spi-topcliff-pch: Add missing descriptions to 'struct pch_spi_data'

spi: spi-topcliff-pch: Add missing descriptions to 'struct pch_spi_data'

Fixes the following W=1 kernel build warning(s):

 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'io_base_addr' not described in 'pch_spi_data'
 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'pkt_tx_buff' not described in 'pch_spi_data'
 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'pkt_rx_buff' not described in 'pch_spi_data'
 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'dma' not described in 'pch_spi_data'
 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'use_dma' not described in 'pch_spi_data'
 drivers/spi/spi-topcliff-pch.c:184: warning: Function parameter or member 'save_total_len' not described in 'pch_spi_data'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200717135424.2442271-12-lee.jones@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>