Makefile: Fix the OpenTitan target

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Makefile

diff --git a/Makefile b/Makefile
index d912813..27157a9 100644
--- a/Makefile
+++ b/Makefile
@@ -73,7 +73,7 @@
 
 .PHONY: flash-opentitan
 flash-opentitan:
-	PLATFORM=opentitan cargo run $(release) --target=riscv32imac-unknown-none-elf --example $(EXAMPLE) $(features)
+	PLATFORM=opentitan cargo run $(release) --target=riscv32imc-unknown-none-elf --example $(EXAMPLE) $(features)
 
 .PHONY: hifive1
 hifive1: