staging: sm750fb: add missing case while setting FB_VISUAL

Switch statement does not contain all cases: 8, 16, 24, 32.
This patch will add missing one (24)

Fixes: 81dee67e ("staging: sm750fb: add sm750 to staging")
Signed-off-by: Matej Dujava <mdujava@kocurkovo.cz>
Link: https://lore.kernel.org/r/1588277366-19354-2-git-send-email-mdujava@kocurkovo.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/sm750fb/sm750.c

@@ -900,6 +900,7 @@ static int lynxfb_set_fbinfo(struct fb_info *info, int index)
 		fix->visual = FB_VISUAL_PSEUDOCOLOR;
 		break;
 	case 16:
+	case 24:
 	case 32:
 		fix->visual = FB_VISUAL_TRUECOLOR;
 		break;