target-openrisc: Fix typename in openrisc_cpu_class_by_name()

Commit 478032a93d908e59085c1ac56f10979942e7dc4f (target-openrisc:
Rename CPU subtypes) suffixed CPU sub-types with "-or32-cpu" but forgot
to update openrisc_cpu_class_by_name(), so that it was still looking for
the types without suffix.

Make target-openrisc running OK by adding the suffix to the model name.

This means it is no longer possible to use -cpu or1200-or32-cpu or
-cpu any-or32-cpu though.

Cc: qemu-stable@nongnu.org
Signed-off-by: Dongxue Zhang <elta.era@gmail.com>
Tested-by: Jia Liu <proljc@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>