leon3: Replace unchecked qdev_init() by qdev_init_nofail()

grlib_irqmp_create(), grlib_gptimer_create() and
grlib_apbuart_create() are helpers to create and realize GRLIB
devices.  Their only caller leon3_generic_hw_init() doesn't check for
failure.  Only the first can actually fail, and only when the caller
fails to set up a pointer property, which is a programming error.

Replace qdev_init() by qdev_init_nofail().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Fabien Chouteau <chouteau@adacore.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
