crypto: lib/chacha20poly1305 - Set SG_MITER_ATOMIC unconditionally

There is no reason for the chacha20poly1305 SG miter code to use
kmap instead of kmap_atomic as the critical section doesn't sleep
anyway.  So we can simply get rid of the preemptible check and
set SG_MITER_ATOMIC unconditionally.

Even if we need to reenable preemption to lower latency we should
be doing that by interrupting the SG miter walk rather than using
kmap.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/crypto/chacha20poly1305.c

@@ -251,9 +251,7 @@ bool chacha20poly1305_crypt_sg_inplace(struct scatterlist *src,
 			poly1305_update(&poly1305_state, pad0, 0x10 - (ad_len & 0xf));
 	}
 
-	flags = SG_MITER_TO_SG;
-	if (!preemptible())
-		flags |= SG_MITER_ATOMIC;
+	flags = SG_MITER_TO_SG | SG_MITER_ATOMIC;
 
 	sg_miter_start(&miter, src, sg_nents(src), flags);