fbdev: ssd1307fb: drop unused function ssd1307fb_write_data()

this patch drops the unused function ssd1307fb_write_data().

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>