[media] cx25821: Cleanup filename assignment code

[media] cx25821: Cleanup filename assignment code

I'm pasting the original code and my proposal on the commit message for
make it easy to compare the two versions.
Line 62 of cx25821-audio-upstream.h contains:
char *_defaultAudioName = "/root/audioGOOD.wav";
Original code after replace kmemdup for kstrdup, and after fix return error
code:
if (dev->input_audiofilename) {
	dev->_audiofilename = kstrdup(dev->input_audiofilename,
				      GFP_KERNEL);
	if (!dev->_audiofilename) {
		err = -ENOMEM;
		goto error;
	}
	/* Default if filename is empty string */
	if (strcmp(dev->input_audiofilename, "") == 0)
		dev->_audiofilename = "/root/audioGOOD.wav";
} else {
	dev->_audiofilename = kstrdup(_defaultAudioName,
				      GFP_KERNEL);
	if (!dev->_audiofilename) {
		err = -ENOMEM;
		goto error;
	}
}
Code proposed in this patch:
if ((dev->input_audiofilename) &&
    (strcmp(dev->input_audiofilename, "") != 0))
	dev->_audiofilename = kstrdup(dev->input_audiofilename,
				      GFP_KERNEL);
else
	dev->_audiofilename = kstrdup(_defaultAudioName,
				      GFP_KERNEL);
if (!dev->_audiofilename) {
	err = -ENOMEM;
	goto error;
}

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>