taget-ppc: Fix read access to IBAT registers higher than IBAT3 Fix the index used to read the IBAT's vector which results in IBAT0..3 instead of IBAT4..N. The bug appeared by saving/restoring contexts including IBATs values. Signed-off-by: Julio Guerra <julio@farjump.io> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>