KVM: arm64: arch_timer: init ret for kvm_timer_enable

virt inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8XA6Z



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Set ret = 0 as default value for kvm_timer_enable.

Signed-off-by: Dongxu Sun <sundongxu3@huawei.com>