net: xfrm: drop check of pols[0] for the second time

!pols[0] is checked earlier.  If we don't return, pols[0] is always
true.  We should drop the check of pols[0] for the second time and the
binary is also smaller.

Before:
   text	   data	    bss	    dec	    hex	filename
  48395	    957	    240	  49592	   c1b8	net/xfrm/xfrm_policy.o

After:
   text	   data	    bss	    dec	    hex	filename
  48379	    957	    240	  49576	   c1a8	net/xfrm/xfrm_policy.o

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>