ppc/: fix some comment spelling errors

ppc/: fix some comment spelling errors

I found that there are many spelling errors in the comments of qemu/target/ppc.
I used spellcheck to check the spelling errors and found some errors in the folder.

Signed-off-by: zhaolichang <zhaolichang@huawei.com>
Reviewed-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20201009064449.2336-3-zhaolichang@huawei.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>