atmel_lcdfb: fix regression with uninitalized fb_info->mm_lock mutex

Remove not needed locking of the fb_info->mm_lock mutex before a
frambuffer is registered.

This fixes a problem with uninitialized the fb_info->mm_lock mutex
introduced by the commit 537a1bf059f " fbdev: add mutex for fb_mmap
locking"

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/atmel_lcdfb.c

@@ -261,6 +261,9 @@ static inline void atmel_lcdfb_free_video_memory(struct atmel_lcdfb_info *sinfo)
 /**
  *	atmel_lcdfb_alloc_video_memory - Allocate framebuffer memory
  *	@sinfo: the frame buffer to allocate memory for
+ * 	
+ * 	This function is called only from the atmel_lcdfb_probe()
+ * 	so no locking by fb_info->mm_lock around smem_len setting is needed.
  */
 static int atmel_lcdfb_alloc_video_memory(struct atmel_lcdfb_info *sinfo)
 {
@@ -270,9 +273,7 @@ static int atmel_lcdfb_alloc_video_memory(struct atmel_lcdfb_info *sinfo)
 
 	smem_len = (var->xres_virtual * var->yres_virtual
 		    * ((var->bits_per_pixel + 7) / 8));
-	mutex_lock(&info->mm_lock);
 	info->fix.smem_len = max(smem_len, sinfo->smem_len);
-	mutex_unlock(&info->mm_lock);
 
 	info->screen_base = dma_alloc_writecombine(info->device, info->fix.smem_len,
 					(dma_addr_t *)&info->fix.smem_start, GFP_KERNEL);