V4L/DVB (6874): removes duplicated KERN_DEBUG flags from dprintk calls in mt312.c

        do { \
                if (debug) printk(KERN_DEBUG "mt312: " args); \
        } while (0)

So no caller need to specify KERN_DEBUG.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>