powerpc/sysfs: Disable writing to PURR in guest mode
powerpc/sysfs: Disable writing to PURR in guest mode

arch/powerpc/kernel/sysfs.c exports PURR with write permission.
This may be valid for kernel in phyp mode. But writing to
the file in guest mode causes crash due to a priviledge violation

Signed-off-by: Madhavan Srinivasan <50c9fed97c2a760bbf32e7fdccf39ca6a997eabd@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>
CC: <4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs