video: sm501fb: Early initialization of mm_lock mutex.

Commit 537a1bf059fa312355696fa6db80726e655e7f17 (fbdev: add mutex for
fb_mmap locking) introduces a ->mm_lock mutex for protecting smem
assignments. Unfortunately in the case of sm501fb these happen quite
early in the initialization code, well before the mutex_init() that takes
place in register_framebuffer(), leading to:

Badness at kernel/mutex.c:207

Pid : 1, Comm: swapper
CPU : 0 Not tainted (2.6.31-rc1-00284-g529ba0d-dirty #2273)

PC is at __mutex_lock_slowpath+0x72/0x1bc
PR is at __mutex_lock_slowpath+0x66/0x1bc
...

matroxfb appears to have the same issue and has solved it with an early
mutex_init(), so we do the same for sm501fb.

Signed-off-by: Paul Mundt <[e-mail]>
Cc: Krzysztof Helt <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/video/sm501fb.c

···
 	if (!fbi)
 		return 0;
 
+	mutex_init(&info->fb[head]->mm_lock);
+
 	ret = sm501fb_init_fb(info->fb[head], head, drvname);
 	if (ret) {
 		dev_err(info->dev, "cannot initialise fb %s\n", drvname);