dma-buf: use vma_pages()

Replace explicit computation of vma page count by a call to
vma_pages().
Also, include <linux/mm.h>

Signed-off-by: Muhammad Falak R Wani <[e-mail]>
Reviewed-by: Eric Engestrom <[e-mail]>
Signed-off-by: Sumit Semwal <[e-mail]>

drivers/dma-buf/dma-buf.c

···
 #include <linux/seq_file.h>
 #include <linux/poll.h>
 #include <linux/reservation.h>
+#include <linux/mm.h>
 
 #include <uapi/linux/dma-buf.h>
 
···
 	dmabuf = file->private_data;
 
 	/* check for overflowing the buffer's size */
-	if (vma->vm_pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
+	if (vma->vm_pgoff + vma_pages(vma) >
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;
 
···
 		return -EINVAL;
 
 	/* check for offset overflow */
-	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < pgoff)
+	if (pgoff + vma_pages(vma) < pgoff)
 		return -EOVERFLOW;
 
 	/* check for overflowing the buffer's size */
-	if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
+	if (pgoff + vma_pages(vma) >
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;