crypto: aesni - xts_crypt() return if walk.nbytes is 0

xts_crypt() code doesn't call kernel_fpu_end() after calling
kernel_fpu_begin() if walk.nbytes is 0. The correct behavior should be
not calling kernel_fpu_begin() if walk.nbytes is 0.

Reported-by: [email protected]
Signed-off-by: Shreyansh Chouhan <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

Author: BK1603

arch/x86/crypto/aesni-intel_glue.c

@@ -849,7 +849,7 @@ static int xts_crypt(struct skcipher_request *req, bool encrypt)
 		return -EINVAL;
 
 	err = skcipher_walk_virt(&walk, req, false);
-	if (err)
+	if (!walk.nbytes)
 		return err;
 
 	if (unlikely(tail > 0 && walk.nbytes < walk.total)) {