sisfb: fix regression with uninitalized fb_info->mm_lock mutex

Remove redundant call to the sisfb_get_fix() before sis frambuffer is
registered.

This fixes a problem with uninitialized the fb_info->mm_lock mutex
introduced by the commit 537a1bf059 " fbdev: add mutex for fb_mmap
locking"

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Tested-by: Wu Zhangjin <wuzhangjin@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/sis/sis_main.c

@@ -6367,7 +6367,6 @@ error_3:	vfree(ivideo->bios_abase);
 		sis_fb_info->fix = ivideo->sisfb_fix;
 		sis_fb_info->screen_base = ivideo->video_vbase + ivideo->video_offset;
 		sis_fb_info->fbops = &sisfb_ops;
-		sisfb_get_fix(&sis_fb_info->fix, -1, sis_fb_info);
 		sis_fb_info->pseudo_palette = ivideo->pseudo_palette;
 
 		fb_alloc_cmap(&sis_fb_info->cmap, 256 , 0);