vm: convert mtdchar mmap to vm_iomap_memory() helper

This is my example conversion of a few existing mmap users.  The mtdchar
case is actually disabled right now (and stays disabled), but I did it
because it showed up on my "git grep", and I was familiar with the code
due to fixing an overflow problem in the code in commit 9c603e53
("mtdchar: fix offset overflow detection").
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/mtd/mtdchar.c

@@ -1159,45 +1159,17 @@ static int mtdchar_mmap(struct file *file, struct vm_area_struct *vma)
 	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_info *mtd = mfi->mtd;
 	struct map_info *map = mtd->priv;
-	resource_size_t start, off;
-	unsigned long len, vma_len;
 
         /* This is broken because it assumes the MTD device is map-based
 	   and that mtd->priv is a valid struct map_info.  It should be
 	   replaced with something that uses the mtd_get_unmapped_area()
 	   operation properly. */
 	if (0 /*mtd->type == MTD_RAM || mtd->type == MTD_ROM*/) {
-		off = get_vm_offset(vma);
-		start = map->phys;
-		len = PAGE_ALIGN((start & ~PAGE_MASK) + map->size);
-		start &= PAGE_MASK;
-		vma_len = get_vm_size(vma);
-
-		/* Overflow in off+len? */
-		if (vma_len + off < off)
-			return -EINVAL;
-		/* Does it fit in the mapping? */
-		if (vma_len + off > len)
-			return -EINVAL;
-
-		off += start;
-		/* Did that overflow? */
-		if (off < start)
-			return -EINVAL;
-		if (set_vm_offset(vma, off) < 0)
-			return -EINVAL;
-		vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
-
 #ifdef pgprot_noncached
-		if (file->f_flags & O_DSYNC || off >= __pa(high_memory))
+		if (file->f_flags & O_DSYNC || map->phys >= __pa(high_memory))
 			vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 #endif
-		if (io_remap_pfn_range(vma, vma->vm_start, off >> PAGE_SHIFT,
-				       vma->vm_end - vma->vm_start,
-				       vma->vm_page_prot))
-			return -EAGAIN;
-
-		return 0;
+		return vm_iomap_memory(vma, map->phys, map->size);
 	}
 	return -ENOSYS;
 #else