riscv: fix nommu_k210_sdcard_defconfig

Instead of an arbitrary delay, use the "rootwait" kernel option to wait
for the mmc root device to be ready.
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Fixes: 7e09fd39 ("riscv: Add Canaan Kendryte K210 SD card defconfig")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/configs/nommu_k210_sdcard_defconfig

@@ -23,7 +23,7 @@ CONFIG_SLOB=y
 CONFIG_SOC_CANAAN=y
 CONFIG_SMP=y
 CONFIG_NR_CPUS=2
-CONFIG_CMDLINE="earlycon console=ttySIF0 rootdelay=2 root=/dev/mmcblk0p1 ro"
+CONFIG_CMDLINE="earlycon console=ttySIF0 root=/dev/mmcblk0p1 rootwait ro"
 CONFIG_CMDLINE_FORCE=y
 # CONFIG_SECCOMP is not set
 # CONFIG_STACKPROTECTOR is not set