target/ppc/mmu-hash32.c: Drop a local variable

target/ppc/mmu-hash32.c: Drop a local variable

In ppc_hash32_xlate() the value of need_prop is checked in two places
but precalculating it does not help because when we reach the first
check we always return and not reach the second place so the value
will only be used once. We can drop the local variable and calculate
it when needed, which makes these checks using it similar to other
places with such checks.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>