Clarify some comments

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index 142c4c6..043bd6a 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1973,7 +1973,7 @@
 
     /* Ensure that target MPI has exactly the same number of limbs
      * as the upper bound, even if the upper bound has leading zeros.
-     * This is necessary for the mbedtls_mpi_lt_mpi_ct() check. */
+     * This is necessary for mbedtls_mpi_core_random. */
     int ret = mbedtls_mpi_resize_clear( X, N->n );
     if( ret != 0 )
         return( ret );

library/bignum_core.c

diff --git a/library/bignum_core.c b/library/bignum_core.c
index a432c2b..770734c 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -163,7 +163,7 @@
     /* min <= least significant limb? */
     unsigned min_le_lsl = 1 ^ mbedtls_ct_mpi_uint_lt( A[0], min );
 
-    /* most significant limbs (excluding 1) are all zero? */
+    /* limbs other than the least significant one are all zero? */
     mbedtls_mpi_uint msll_mask = 0;
     for( size_t i = 1; i < A_limbs; i++ )
         msll_mask |= A[i];