mm/mempolicy: remove unneeded out label

We can use unlock label to unlock ptl and return ret directly to remove
the unneeded out label and reduce the size of mempolicy.o.  No functional
change intended.

[Before]
   text	   data	    bss	    dec	    hex	filename
  26702	   3972	   6168	  36842	   8fea	mm/mempolicy.o

[After]
   text	   data	    bss	    dec	    hex	filename
  26662	   3972	   6168	  36802	   8fc2	mm/mempolicy.o

Link: https://lkml.kernel.org/r/20220719115233.6706-1-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>