[media] omap_vout: Get rid of a few warnings

[media] omap_vout: Get rid of a few warnings

drivers/media/platform/omap/omap_vout.c: In function 'omapvid_setup_overlay':
drivers/media/platform/omap/omap_vout.c:372:29: warning: variable 'pixheight' set but not used [-Wunused-but-set-variable]
  int cropheight, cropwidth, pixheight, pixwidth;
                             ^
drivers/media/platform/omap/omap_vout.c: In function 'vidioc_s_ctrl':
drivers/media/platform/omap/omap_vout.c:1454:24: warning: variable 'ovl' set but not used [-Wunused-but-set-variable]
   struct omap_overlay *ovl;
                        ^
drivers/media/platform/omap/omap_vout.c: In function 'vidioc_reqbufs':
drivers/media/platform/omap/omap_vout.c:1492:55: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
  if ((req->type != V4L2_BUF_TYPE_VIDEO_OUTPUT) || (req->count < 0))
                                                       ^

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