fbdev: atafb: Remove obsolete module support

CONFIG_FB_ATARI is bool, hence the Atari frame buffer driver cannot be
built as a module.  In addition, the module support code refers to a
function atafb_deinit(), which never existed.

Replace module_init() by device_initcall().

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Michael Schmitz <schmitzmic@gmail.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>