Fix missing-prototype errors in tests/suites

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/tests/suites/test_suite_entropy.function b/tests/suites/test_suite_entropy.function
index 5ac65fc..c89c26c 100644
--- a/tests/suites/test_suite_entropy.function
+++ b/tests/suites/test_suite_entropy.function
@@ -65,7 +65,7 @@
  */
 static unsigned char buffer_seed[MBEDTLS_ENTROPY_BLOCK_SIZE];
 
-int buffer_nv_seed_read(unsigned char *buf, size_t buf_len)
+static int buffer_nv_seed_read(unsigned char *buf, size_t buf_len)
 {
     if (buf_len != MBEDTLS_ENTROPY_BLOCK_SIZE) {
         return -1;
@@ -75,7 +75,7 @@
     return 0;
 }
 
-int buffer_nv_seed_write(unsigned char *buf, size_t buf_len)
+static int buffer_nv_seed_write(unsigned char *buf, size_t buf_len)
 {
     if (buf_len != MBEDTLS_ENTROPY_BLOCK_SIZE) {
         return -1;
@@ -111,7 +111,7 @@
     return 0;
 }
 
-int read_nv_seed(unsigned char *buf, size_t buf_len)
+static int read_nv_seed(unsigned char *buf, size_t buf_len)
 {
     FILE *f;