KVM: arm64: Fix error return code in init_hyp_mode()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: eeeee719 ("KVM: arm64: Bootstrap PSCI SMC handler in nVHE EL2")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210406121759.5407-1-wangwensheng4@huawei.com