wilc1000: Remove misleading USE_SPI_DMA macro

The USE_SPI_DMA macro name suggests that it could be set to 1 to
control whether or not SPI DMA should be used.  However, that's not
what it does.  If set to 1, it'll set the SPI messages'
"is_dma_mapped" flag to true, even though the tx/rx buffers aren't
actually DMA mapped by the driver.  In other words, setting this flag
to 1 will break the driver.

Best to clean up this confusion by removing the macro altogether.
There is no need to explicitly initialize "is_dma_mapped" because the
message is cleared to zero anyhow, so "is_dma_mapped" is set to false
by default.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Acked-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211207002453.3193737-1-davidm@egauge.net