[media] bdisp: remove needless check

As reported by smatch:
	drivers/media/platform/sti/bdisp/bdisp-v4l2.c:947 bdisp_s_selection() warn: unsigned 'out.width' is never less than zero.
	drivers/media/platform/sti/bdisp/bdisp-v4l2.c:947 bdisp_s_selection() warn: unsigned 'out.height' is never less than zero.
Indeed, width and height are unsigned.

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>