can: mcp251x: fix support for half duplex SPI host controllers

can: mcp251x: fix support for half duplex SPI host controllers

Some SPI host controllers do not support full-duplex SPI transfers.

The function mcp251x_spi_trans() does a full duplex transfer. It is
used in several places in the driver, where a TX half duplex transfer
is sufficient.

To fix support for half duplex SPI host controllers, this patch
introduces a new function mcp251x_spi_write() and changes all callers
that do a TX half duplex transfer to use mcp251x_spi_write().

Fixes: e0e25001d088 ("can: mcp251x: add support for half duplex controllers")
Link: https://lore.kernel.org/r/[email protected]
Cc: Tim Harvey <[email protected]>
Tested-By: Tim Harvey <[email protected]>
Reported-by: Gerhard Bertelsmann <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>