HSI: cmt_speech: use vma_pages().

Replace explicit computation of vma page count by a call to
vma_pages()
Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

drivers/hsi/clients/cmt_speech.c

@@ -1275,7 +1275,7 @@ static int cs_char_mmap(struct file *file, struct vm_area_struct *vma)
 	if (vma->vm_end < vma->vm_start)
 		return -EINVAL;
 
-	if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) != 1)
+	if (vma_pages(vma) != 1)
 		return -EINVAL;
 
 	vma->vm_flags |= VM_IO | VM_DONTDUMP | VM_DONTEXPAND;