cppcheck: fixes from scan

wolfssl_sce_unit_test.c:
  sce_crypt_Sha_AesCbcGcm_multitest(): duplicate condition
ssl_asn1.c:
  wolfSSL_i2t_ASN1_OBJECT(): done is not needed
  MonthStr(): fix bounds check on i
woolfcrypt_test.c, test_main.c, wolfssl_tsip_unit_test.c, devices.c,
aes.c, des3.c:
  Variable not used.
asn.c:
DecodeSubjKeyId(): sz is unsigned - check for less than zero does
nothing
kcapi_rsa.c:
  KcapiRsa_Decrypt(): fix ret check by using else
  KcapiRsa_Encrypt(): make same change for consistency
kcapi_hash.c:
  KcapiHashFinal(): move ret into #ifdef where it is needed
stm32.c:
wc_Stm32_Hash_GetDigest(): i redeclared with different type - use ii
instead
bio.c, conf.c:
  XFREE checks for NULL

Reduce scope of varialbes.
Condition same.

wolfcrypt/src/fe_operations.c

@@ -142,7 +142,6 @@ int curve25519(byte* q, const byte* n, const byte* p)
   fe tmp1 = {0};
   int pos = 0;
   unsigned int swap = 0;
-  unsigned int b = 0;
 
   /* Clamp already done during key generation and import */
 #if 0
@@ -163,6 +162,7 @@ int curve25519(byte* q, const byte* n, const byte* p)
 
   swap = 0;
   for (pos = 254;pos >= 0;--pos) {
+    unsigned int b;
 #if 0
     b = e[pos / 8] >> (pos & 7);
 #else