media: saa7134: avoid a shift overflow

As reported by smatch:
	drivers/media/pci/saa7134//saa7134-tvaudio.c:686 saa_dsp_writel() warn: should 'reg << 2' be a 64 bit type?

On a 64-bits Kernel, the shift might be bigger than 32 bits.

In real, this should never happen, but let's shut up the warning.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/pci/saa7134/saa7134-tvaudio.c

@@ -683,7 +683,8 @@ int saa_dsp_writel(struct saa7134_dev *dev, int reg, u32 value)
 {
 	int err;
 
-	audio_dbg(2, "dsp write reg 0x%x = 0x%06x\n", reg << 2, value);
+	audio_dbg(2, "dsp write reg 0x%x = 0x%06x\n",
+		  (reg << 2) & 0xffffffff, value);
 	err = saa_dsp_wait_bit(dev,SAA7135_DSP_RWSTATE_WRR);
 	if (err < 0)
 		return err;