lib/mpi: mpi_write_sgl(): purge redundant pointer arithmetic

Within the copying loop in mpi_write_sgl(), we have

  if (lzeros) {
    ...
    p -= lzeros;
    y = lzeros;
  }
  p = p - (sizeof(alimb) - y);

If lzeros == 0, then y == 0, too. Thus, lzeros gets subtracted and added
back again to p.

Purge this redundancy.
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/mpi/mpicoder.c

@@ -407,12 +407,11 @@ int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 			mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 				+ lzeros;
 			*limb1 = *limb2;
-			p -= lzeros;
 			y = lzeros;
 			lzeros = 0;
 		}
 
-		p = p - (sizeof(alimb) - y);
+		p = p - sizeof(alimb);
 
 		for (x = 0; x < sizeof(alimb) - y; x++) {
 			if (!buf_len) {