[media] omap3isp: fix compiler warning

This patch fixes this compiler warning:
  drivers/media/video/omap3isp/isp.c: In function 'isp_isr_dbg':
  drivers/media/video/omap3isp/isp.c:392:2: warning: zero-length
   gnu_printf format string

Signed-off-by: Sanjeev Premi <premi@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>