powerpc/eeh: EEH_PE_ISOLATED not reflect HW state

When doing PE reset, EEH_PE_ISOLATED is cleared unconditionally.
However, We should remove that if the PE reset has cleared the
frozen state successfully. Otherwise, the flag should be kept.
The patch fixes the issue.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>