mm/mmap: Fix VM_LOCKED check in do_vmi_align_munmap()

6.1 backport of the patch [1] uses 'next' vma instead of 'split' vma.
Fix the mistake.

[1] commit 606c812e ("mm/mmap: Fix error path in do_vmi_align_munmap()")

Fixes: a149174f ("mm/mmap: Fix error path in do_vmi_align_munmap()")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>