xilinx_spips: Use 8 dummy cycles with the QIOR/QIOR4 commands

Use 8 dummy cycles (4 dummy bytes) with the QIOR/QIOR4 commands in legacy mode
for matching what is expected by Micron (Numonyx) flashes (the default target
flash type of the QSPI).

Signed-off-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Tested-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 20180223232233.31482-3-frasse.iglesias@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/ssi/xilinx_spips.c

@@ -577,7 +577,7 @@ static int xilinx_spips_num_dummies(XilinxQSPIPS *qs, uint8_t command)
         return 2;
     case QIOR:
     case QIOR_4:
-        return 5;
+        return 4;
     default:
         return -1;
     }