Fix include guards to match presubmit expectations

Test: pw presubmit --full --step include_guard
Change-Id: Iae91c44a9d04148b66a4c301d2325969e213afa1
Reviewed-on: https://pigweed-review.googlesource.com/c/open-dice/+/162997
Reviewed-by: Andrew Scull <ascull@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Darren Krahn <dkrahn@google.com>
diff --git a/third_party/mbedtls/custom_config.h b/third_party/mbedtls/custom_config.h
index 24d5418..3044667 100644
--- a/third_party/mbedtls/custom_config.h
+++ b/third_party/mbedtls/custom_config.h
@@ -12,8 +12,8 @@
 // License for the specific language governing permissions and limitations under
 // the License.
 
-#ifndef MBEDTLS_CONFIG_H
-#define MBEDTLS_CONFIG_H
+#ifndef THIRD_PARTY_MBEDTLS_CUSTOM_CONFIG_H_
+#define THIRD_PARTY_MBEDTLS_CUSTOM_CONFIG_H_
 
 /* mbed TLS feature support */
 #define MBEDTLS_DEPRECATED_REMOVED
@@ -40,4 +40,4 @@
 
 #include "mbedtls/check_config.h"
 
-#endif /* MBEDTLS_CONFIG_H */
+#endif /* THIRD_PARTY_MBEDTLS_CUSTOM_CONFIG_H_ */