[media] saa7134-ts: use pr_fmt() at the debug macro

instead of using dev->name, let's use pr_fmt() like on the
other parts of saa7134. Also, rename the debug macro to
ts_dbg() to match the namespace for the debug macros.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>