[media] stkwebcam: Fix sparse warning on undeclared symbol
The sparse warning is:
"drivers/media/usb/stkwebcam/stk-webcam.c:59:5:
warning: symbol 'first_init' was not declared. Should it be static?"
Declare variable 'first_init' as static and local to the function.
Found by Hans Verkuil's daily build. Tested by compilation only.