spi: spi-gpio.c tests SPI_MASTER_NO_RX bit twice, but not SPI_MASTER_NO_TX

The SPI_MASTER_NO_TX bit (can't do buffer write) wasn't tested.  This
code was introduced in commit 3c8e1a84 (spi/spi-gpio: add support for
controllers without MISO or MOSI pin).  This patch fixes a bug in
choosing which transfer ops to use.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>