powerpc/oops: Fix missing pr_cont()s in show_regs()

Fix up our oops output by converting continuation lines to use
pr_cont(). Some of these are dubious, eg. printing a continuation line
which starts with a newline, but seem to work OK for now. This whole
function needs a rewrite in the next release.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>