powerpc/mm: convert coprocessor fault to lock_mm_and_find_vma()

This is one of the simple cases, except there's no pt_regs pointer.
Which is fine, as lock_mm_and_find_vma() is set up to work fine with a
NULL pt_regs.

Powerpc already enabled LOCK_MM_AND_FIND_VMA for the main CPU faulting,
so we can just use the helper without any extra work.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/mm/copro_fault.c

@@ -33,19 +33,11 @@ int copro_handle_mm_fault(struct mm_struct *mm, unsigned long ea,
 	if (mm->pgd == NULL)
 		return -EFAULT;
 
-	mmap_read_lock(mm);
-	ret = -EFAULT;
-	vma = find_vma(mm, ea);
+	vma = lock_mm_and_find_vma(mm, ea, NULL);
 	if (!vma)
-		goto out_unlock;
-
-	if (ea < vma->vm_start) {
-		if (!(vma->vm_flags & VM_GROWSDOWN))
-			goto out_unlock;
-		if (expand_stack(vma, ea))
-			goto out_unlock;
-	}
+		return -EFAULT;
 
+	ret = -EFAULT;
 	is_write = dsisr & DSISR_ISSTORE;
 	if (is_write) {
 		if (!(vma->vm_flags & VM_WRITE))