crypto: fix af_alg_make_sg() conversion to iov_iter

Commit 1d10eb2f15 ("crypto: switch af_alg_make_sg() to iov_iter")
broke af_alg_make_sg() and skcipher_recvmsg() in the process of moving
them to the iov_iter interfaces.  The 'npages' calculation in the formar
calculated the number of *bytes* in the pages, and in the latter case
the conversion didn't re-read the value of 'ctx->used' after waiting for
it to become non-zero.

This reverts to the original code for both these cases.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

crypto/af_alg.c

@@ -348,7 +348,7 @@ int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len)
 	if (n < 0)
 		return n;
 
-	npages = PAGE_ALIGN(off + n);
+	npages = (off + n + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (WARN_ON(npages == 0))
 		return -EINVAL;