vl.c: allow for repeated -sd arguments

Allows for repeating of -sd arguments in the same way as -pflash and -mtdblock.

Acked-by: Igor Mitsyanko <i.mitsyanko@samsung.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/vl.c b/vl.c
index febd2ea..c03edf1 100644
--- a/vl.c
+++ b/vl.c
@@ -2994,7 +2994,7 @@
                 drive_add(IF_MTD, -1, optarg, MTD_OPTS);
                 break;
             case QEMU_OPTION_sd:
-                drive_add(IF_SD, 0, optarg, SD_OPTS);
+                drive_add(IF_SD, -1, optarg, SD_OPTS);
                 break;
             case QEMU_OPTION_pflash:
                 drive_add(IF_PFLASH, -1, optarg, PFLASH_OPTS);