drivers/ata/pata_mpc52xx.c: clean up error handling code

This patch makes a number of changes with respect to the error-handling
code:

* Remove cleanup calls for the devm functions in both the error handling
  code and the remove function.  This cleanup is done automatically.

* The previous change simplifies the cleanup code at the end of the
  function such that there is nothing to do on the failure of the call to
  devm_ioremap.  So it is changed to just return directly.

* There is no need for the ifs in the cleanup code at the end of the
  function, because in each case the cleanup needed is statically
  known.  Drop the ifs, add new err labels, and drop the initializations of
  the tested variables to NULL.

* Change the call to request_irq to a call to devm_request_irq, so that it
  is cleaned up on exit.

* Cause the return value of devm_request_irq to go into the returned
  variable rv rather than the unused variable ret.  Drop ret.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>