iwlwifi: fix compile warning

When iwlwifi is compiled w/o debug, we get
this warning:
iwl-agn.c: In function ‘iwlagn_load_firmware’:
iwl-agn.c:2014: warning: passing argument 3 of ‘iwl_print_hex_dump’ discards qualifiers from pointer target type
iwl-debug.h:73: note: expected ‘void *’ but argument is of type ‘const u8 *’

because the const qualifier is missing in the
inline stub. Fix this.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NWey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-debug.h

@@ -71,7 +71,7 @@ do {                                            			\
 #define IWL_DEBUG(__priv, level, fmt, args...)
 #define IWL_DEBUG_LIMIT(__priv, level, fmt, args...)
 static inline void iwl_print_hex_dump(struct iwl_priv *priv, int level,
-				      void *p, u32 len)
+				      const void *p, u32 len)
 {}
 #endif				/* CONFIG_IWLWIFI_DEBUG */