powerpc/fadump: Trivial fix of spelling mistake, clean up message

Fix trivial spelling mistake "rgistration". Also use pr_err()
instead of printk() and unsplit the string to keep it all on one
line.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
[mpe: Keep rc on the same line, splitting it doesn't help]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>