qemu-native: fix build

[twoerner]

The risc-v qemu recipe wasn't pointing at a valid commit from the github.com/riscv/riscv-qemu.git repository.

Tweak how the QEMU_TARGETS variable is populated in order to pick a valid target. IOW riscv -> riscv64.

Signed-off-by: Trevor Woerner [email protected]