MIPS: Return true/false (not 1/0) from bool functions

./arch/mips/kernel/uprobes.c:261:8-9: WARNING: return of 0/1 in function
'arch_uprobe_skip_sstep' with return type bool
./arch/mips/kernel/uprobes.c:78:10-11: WARNING: return of 0/1 in
function 'is_trap_insn' with return type bool
./arch/mips/kvm/mmu.c:489:9-10: WARNING: return of 0/1 in function
'kvm_test_age_gfn' with return type bool
./arch/mips/kvm/mmu.c:445:8-9: WARNING: return of 0/1 in function
'kvm_unmap_gfn_range' with return type bool

Signed-off-by: Huilong Deng <denghuilong@cdjrlc.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>