Mask value read from SPI_ADRS_DMA_WRITE_CTRL in p54spi_wait_bit.
 Without this, 'fw_upload not allowed to DMA write' is observed at both N800 and N810.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>