video: ssd1307fb: Remove redundant forward declaration

There is no need to have forward declaration of struct ssd1307fb_par.
Drop it for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200324170532.44384-5-andriy.shevchenko@linux.intel.com