The existing qspi for stm32 implementation can only send a spi command with
exactly 0 or 2 data bytes. Certain spiflash chips (e.g. AT25SF321B) have
commands that only take a single data byte, and will ignore the command if
more than that is sent. This commit allows sending a command with a single
data byte.
Signed-off-by: Victor Rajewski <victor@allumeenergy.com.au>