gsm/gsm48.h: drop meaningless 'const' from gsm48_mi_to_string()

Change-Id: I5eb17edadf89ac47b4ca86c9e822037f7c0e518e
diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index c97337b..2d6deb5 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -741,8 +741,7 @@
  *           Depending on the MI type and amount of output buffer, this may return
  *           the nr of written bytes, or the written strlen(), or the snprintf()
  *           style strlen()-if-the-buffer-were-large-enough. */
-int gsm48_mi_to_string(char *string, const int str_len, const uint8_t *mi,
-		       const int mi_len)
+int gsm48_mi_to_string(char *string, int str_len, const uint8_t *mi, int mi_len)
 {
 	int rc;
 	uint8_t mi_type;