Platform: Fix issues of cppcheck under platform/ext/common.

As programming issues found in static check, those issues
shall be fixed to make code more stable.

Signed-off-by: Chendi Sun <chendi.sun@arm.com>
Change-Id: I17e7bc0682f3d5ea9933ebb67e9ebd14cda12a0a
diff --git a/platform/ext/common/provisioning.c b/platform/ext/common/provisioning.c
index 358d772..01f482e 100644
--- a/platform/ext/common/provisioning.c
+++ b/platform/ext/common/provisioning.c
@@ -29,7 +29,9 @@
     uint8_t iak[32];
     uint32_t iak_len;
     uint32_t iak_type;
+#if ATTEST_INCLUDE_COSE_KEY_ID
     uint8_t iak_id[32];
+#endif /* ATTEST_INCLUDE_COSE_KEY_ID */
 
     uint8_t boot_seed[32];
     uint8_t implementation_id[32];
@@ -70,8 +72,10 @@
     /* IAK type */
     PSA_ECC_FAMILY_SECP_R1,
 #endif /* SYMMETRIC_INITIAL_ATTESTATION */
+#if ATTEST_INCLUDE_COSE_KEY_ID
     /* IAK id */
     "kid@trustedfirmware.example",
+#endif /* ATTEST_INCLUDE_COSE_KEY_ID */
     /* boot seed */
     {
         0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7,