powerpc/pseries: Cleanup on pseries_eeh_get_state()

This cleans up pseries_eeh_get_state(), no functional changes:

   * Return EEH_STATE_NOT_SUPPORT early when the 2nd RTAS output
     argument is zero to avoid nested if statements.
   * Skip clearing bits in the PE state represented by variable
     "result" to simplify the code.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>