iwlwifi: compilation error when CONFIG_IWLWIFI_DEBUG is not set

CC [M]  drivers/net/wireless/iwlwifi/iwl-rfkill.o
drivers/net/wireless/iwlwifi/iwl-led.c: In function 'iwl_led_brightness_set':
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: 'led_type_str' undeclared (first use in this function)
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: (Each undeclared identifier is reported only once
drivers/net/wireless/iwlwifi/iwl-led.c:198: error: for each function it appears in.)

The problem is that led_type_str is defined under CONFIG_IWLWIFI_DEBUG
while IWL_DEBUG is a static inline function in this case. Replace it
with macro.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>