fbdev: omapfb: off by one in omapfb_register_client()

The omapfb_register_client[] array has OMAPFB_PLANE_NUM elements so the
> should be >= or we are one element beyond the end of the array.

Fixes: 8b08cf2b ("OMAP: add TI OMAP framebuffer driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Imre Deak <imre.deak@solidboot.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>