powerpc/powernv: Cleanup on EEH comments

This applies cleanup on eeh-powernv.c, no functional changes:

   * Remove unnecessary comments and empty line.
   * Correct inaccurate comments.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>