hv: add brackets to make operator expression more readable

v1-v2:
Bypass this case:
When binary arithmetic operators of different precedence (e.g. '+'
and '*') are mixed in an expression, parentheses are added to the
sub-expressions using the operator with a higher precedence.

v1:
The operator precedence rules are complicated and it is easy to make a mistake.
So add brackets to make operator expression more readable.

Tracked-On: #861
Signed-off-by: Li, Fei1 <fei1.li@intel.com>

hypervisor/lib/crypto/mbedtls/hkdf.c

@@ -167,7 +167,7 @@ int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
             goto exit;
         }
 
-        num_to_copy = i != n ? hash_len : okm_len - where;
+        num_to_copy = (i != n) ? hash_len : (okm_len - where);
         memcpy_s( okm + where, num_to_copy, t, num_to_copy );
         where += hash_len;
         t_len = hash_len;