[syzbot] riscv/fixes build error

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9abf2313adc1 Linux 6.1-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
console output: https://syzkaller.appspot.com/x/log.txt?x=152b6b6a880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9631ed0b9757aaab
dashboard link: https://syzkaller.appspot.com/bug?extid=9d8dc6c2d48bbc419bb4
compiler:       riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: riscv64

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9d8dc6c2d48bbc419bb4 at syzkaller.appspotmail.com

arch/riscv/kvm/vcpu.c:269: undefined reference to `riscv_cbom_block_size'
riscv64-linux-gnu-ld: arch/riscv/kvm/vcpu.c:269: undefined reference to `riscv_cbom_block_size'

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