video: fbdev: atari: Fix inverse handling

Currently, the "inverse" option does not do anything, as it just sets a
flag, which is further unused.

Fix this by calling fb_invert_cmaps() instead, like other drivers do.
As this only affects the console colormap, this does not affect X.
Update the documentation to match the actual behavior.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Tested-by: Michael Schmitz <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>

Documentation/m68k/kernel-options.rst

···
 4.1.2) inverse
 --------------
 
-Invert the display. This affects both, text (consoles) and graphics
-(X) display. Usually, the background is chosen to be black. With this
+Invert the display. This affects only text consoles.
+Usually, the background is chosen to be black. With this
 option, you can make the background white.
 
 4.1.3) font

drivers/video/fbdev/atafb.c

···
 #endif /* ATAFB_EXT */
 
 
-static int inverse;
-
 /*
  * struct fb_ops {
  *	* open/release and usage marking
···
 			default_par = temp;
 			mode_option = this_opt;
 		} else if (!strcmp(this_opt, "inverse"))
-			inverse = 1;
+			fb_invert_cmaps();
 		else if (!strncmp(this_opt, "hwscroll_", 9)) {
 			hwscroll = simple_strtoul(this_opt + 9, NULL, 10);
 			if (hwscroll < 0)