Bluetooth: SPI: retry spi_transceive calls if invalid

spi_transceive can return successfuly even if the data provided by the
slave is invalid, so check if the content is correct and retry until a
valid data is available.

Change-Id: Ia951de391e0b24c5b41eeabfb5c10b056d32b62e
Signed-off-by: Ricardo Salveti <ricardo.salveti@linaro.org>