V4L/DVB (5391): Saa7134: Clean up printk()s

Change some debug messages from printk() to dprintk().

Add KERN_WARNING and KERN_ERR level indicators to other printk()s that
lacked them.

Format printk lines with consistent ("%s/dvb: ", dev->name) prefix.

Fixed dprintk macro, which had an if with no else that wasn't protected
with a do {} while(0) block.  That leads to "if(...) dprintk(); else" not
doing what one would expect.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Acked-by: Hartmut Hackmann <hartmut.hackmann@t-online.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>