spi: altera: fix return value for altera_spi_txrx()

spi: altera: fix return value for altera_spi_txrx()

This patch fixes the return value for altera_spi_txrx. It should return
1 for interrupt transfer mode, and return 0 for polling transfer mode.

The altera_spi_txrx() implements the spi_controller.transfer_one
callback. According to the spi-summary.rst, the transfer_one should
return 0 when transfer is finished, return 1 when transfer is still in
progress.

Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/1609219662-27057-2-git-send-email-yilun.xu@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>