library: debug: make mbedtls_debug_print_ecp() internal

Remove the public definition of mbedtls_debug_print_ecp(). The function
is only used internally in debug.c, so we can then make the function
static.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/debug.c b/library/debug.c
index 71e0642..d36b041 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -168,9 +168,9 @@
 }
 
 #if defined(MBEDTLS_ECP_LIGHT)
-void mbedtls_debug_print_ecp(const mbedtls_ssl_context *ssl, int level,
-                             const char *file, int line,
-                             const char *text, const mbedtls_ecp_point *X)
+static void mbedtls_debug_print_ecp(const mbedtls_ssl_context *ssl, int level,
+                                    const char *file, int line,
+                                    const char *text, const mbedtls_ecp_point *X)
 {
     char str[DEBUG_BUF_SIZE];