powerpc: pseries: Fix kexec on machines with more than 4TB of RAM

commit bed9a315 upstream.

On a box with 8TB of RAM the MMU hashtable is 64GB in size. That
means we have 4G PTEs. pSeries_lpar_hptab_clear was using a signed
int to store the index which will overflow at 2G.

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>