KVM: PPC: Book3S HV: Use consistent type for return value of kvm_age_rmapp()

The return value type defined in the function kvm_age_rmapp() is
"bool", but the return value type defined in the implementation of the
function kvm_age_rmapp() is "int".

Change the return value type to "bool".

Signed-off-by: Bo Liu <liubo03@inspur.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220401065252.36472-1-liubo03@inspur.com