[media] stk1135: fix two warnings added by changeset 76e05987

drivers/media/usb/gspca/stk1135.c:615:6: warning: no previous prototype for 'stk1135_try_fmt' [-Wmissing-prototypes]
 void stk1135_try_fmt(struct gspca_dev *gspca_dev, struct v4l2_format *fmt)
      ^
drivers/media/usb/gspca/stk1135.c:627:5: warning: no previous prototype for 'stk1135_enum_framesizes' [-Wmissing-prototypes]
 int stk1135_enum_framesizes(struct gspca_dev *gspca_dev,

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>