gsm/gsm_utils.h: fix argument type of gsm_chan_t_name()

The actual value-string array 'gsm_chan_t_names' describes
the enum values of 'gsm_chan_t', not 'gsm48_chan_mode'.

Change-Id: Ifc2121b23fb8d07589cc5b7aa8fbf4e27eb6b72b
Fixes: CID#188831, CID#188825
diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index 37df665..7a5da9a 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -230,7 +230,7 @@
 };
 
 extern const struct value_string gsm_chan_t_names[];
-static inline const char *gsm_chan_t_name(enum gsm48_chan_mode val)
+static inline const char *gsm_chan_t_name(enum gsm_chan_t val)
 { return get_value_string(gsm_chan_t_names, val); }
 
 /* Deprectated functions */