V4L/DVB (6147): Pwc: Fix a broken debug message

Commit 85237f20

 introduced the
following warning (with CONFIG_USB_PWC_DEBUG=y):
drivers/media/video/pwc/pwc-if.c: In function "pwc_video_close":
drivers/media/video/pwc/pwc-if.c:1211: warning: "i" may be used uninitialized in this function

This is true, and can cause a broken debug message to be logged.
Here's a fix.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>