target/i386/kvm: Return -1 when kvm_msr_energy_thread_init() fails

target/i386/kvm: Return -1 when kvm_msr_energy_thread_init() fails

It is common practice to return a negative value (like -1) to indicate
an error, and other functions in kvm_arch_init() follow this style.

To avoid confusion (sometimes returned -1 indicates failure, and
sometimes -1, in a same function), return -1 when
kvm_msr_energy_thread_init() fails.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20241106030728.553238-10-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>