KVM: selftests: Make reclaim_period_ms input always be positive

reclaim_period_ms used to be positive only but the commit 0001725d
("KVM: selftests: Add atoi_positive() and atoi_non_negative() for input
validation") incorrectly changed it to non-negative validation.

Change validation to allow only positive input.

Fixes: 0001725d ("KVM: selftests: Add atoi_positive() and atoi_non_negative() for input validation")
Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reported-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230111183408.104491-1-vipinsh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>