gigaset: silence GCC warning for unused 'format_ie'

Building Gigaset's CAPI support without Gigaset's debugging enabled
triggers this GCC warning:
    'format_ie' defined but not used [-Wunused-function]

Silence this warning by wrapping format_ie() in an "#ifdef
CONFIG_GIGASET_DEBUG" and "#endif" pair.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/capi.c

@@ -288,6 +288,7 @@ static inline void dump_rawmsg(enum debuglevel level, const char *tag,
  * format CAPI IE as string
  */
 
+#ifdef CONFIG_GIGASET_DEBUG
 static const char *format_ie(const char *ie)
 {
 	static char result[3 * MAX_FMT_IE_LEN];
@@ -313,6 +314,7 @@ static const char *format_ie(const char *ie)
 	*--pout = 0;
 	return result;
 }
+#endif
 
 /*
  * emit DATA_B3_CONF message