Use empty inline functions instead of empty #define. Fix for "unused variable"
as reported below:

tree:   git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-next.git master
head:   167bf96d
commit: 871d8c4b [45/62] wil6210: fix usage of print_hex_dump_debug
config: i386-allyesconfig
reproduce:
  git checkout 871d8c4b
  make ARCH=i386  allyesconfig
  make ARCH=i386

All warnings:

   drivers/net/wireless/ath/wil6210/wmi.c: In function 'wmi_evt_rx_mgmt':

>> drivers/net/wireless/ath/wil6210/wmi.c:341:10: warning: unused variable 'ie_len' [-Wunused-variable]
      size_t ie_len = d_len - offsetof(struct ieee80211_mgmt,
             ^

>> drivers/net/wireless/ath/wil6210/wmi.c:340:13: warning: unused variable 'ie_buf' [-Wunused-variable]
      const u8 *ie_buf = rx_mgmt_frame->u.beacon.variable;
                ^

vim +/ie_len +341 drivers/net/wireless/ath/wil6210/wmi.c

2be7d22f Vladimir Kondratiev 2012-12-20  334
2be7d22f Vladimir Kondratiev 2012-12-20  335    if (ieee80211_is_beacon(fc) || ieee80211_is_probe_resp(fc)) {
2be7d22f Vladimir Kondratiev 2012-12-20  336            struct cfg80211_bss *bss;
8eea944a Vladimir Kondratiev 2014-06-16  337            u64 tsf = le64_to_cpu(rx_mgmt_frame->u.beacon.timestamp);
8eea944a Vladimir Kondratiev 2014-06-16  338            u16 cap = le16_to_cpu(rx_mgmt_frame->u.beacon.capab_info);
8eea944a Vladimir Kondratiev 2014-06-16  339            u16 bi = le16_to_cpu(rx_mgmt_frame->u.beacon.beacon_int);
8eea944a Vladimir Kondratiev 2014-06-16  340            const u8 *ie_buf = rx_mgmt_frame->u.beacon.variable;
8eea944a Vladimir Kondratiev 2014-06-16  341            size_t ie_len = d_len - offsetof(struct ieee80211_mgmt,
8eea944a Vladimir Kondratiev 2014-06-16  342                                             u.beacon.variable);
8eea944a Vladimir Kondratiev 2014-06-16  343            wil_dbg_wmi(wil, "Capability info : 0x%04x\n", cap);
8eea944a Vladimir Kondratiev 2014-06-16  344            wil_dbg_wmi(wil, "TSF : 0x%016llx\n", tsf);

:::::: The code at line 341 was first introduced by commit
:::::: 8eea944a wil6210: print more info about BSS found
Signed-off-by: NVladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>