pseries: Clean up error reporting in ppc_spapr_init()

This function includes a number of explicit fprintf()s for errors.
Change these to use error_report() instead.

Also replace the single exit(EXIT_FAILURE) with an explicit exit(1), since
the latter is the more usual idiom in qemu by a large margin.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Markus Armbruster <armbru@redhat.com>