xilinx_spips: Correct the number of dummy cycles for the FAST_READ_4 cmd

xilinx_spips: Correct the number of dummy cycles for the FAST_READ_4 cmd

Correct the number of dummy cycles required by the FAST_READ_4 command (to
be eight, one dummy byte).

Fixes: ef06ca3946 ("xilinx_spips: Add support for RX discard and RX drain")
Suggested-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20200218113350.6090-1-frasse.iglesias@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>