psa: cipher: Fix comment type

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/psa/crypto_builtin_cipher.h b/include/psa/crypto_builtin_cipher.h
index 72d3e8d..0fd577a 100644
--- a/include/psa/crypto_builtin_cipher.h
+++ b/include/psa/crypto_builtin_cipher.h
@@ -37,7 +37,7 @@
 #endif
 
 typedef struct {
-    /** Context structure for the Mbed TLS cipher implementation. */
+    /* Context structure for the Mbed TLS cipher implementation. */
     psa_algorithm_t alg;
     uint8_t iv_size;
     uint8_t block_size;