KVM: x86: Remove unnecessary initialization in kvm_vm_ioctl_set_msr_filter()

Do not initialize the value of `r`, as it will be overwritten.

Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20230107001256.2365304-6-mhal@rbox.co


Signed-off-by: Sean Christopherson <seanjc@google.com>