parisc: Fix locking in pdc_iodc_print() firmware call

Utilize pdc_lock spinlock to protect parallel modifications of the
iodc_dbuf[] buffer, check length to prevent buffer overflow of
iodc_dbuf[], drop the iodc_retbuf[] buffer and fix some wrong
indentings.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: <stable@vger.kernel.org> # 6.0+