ath9k_hw: index out of bounds

Check whether index is within bounds before testing the element

Both spurChans arrays in modalHeader5G and modalHeader2G have 5 elements,
AR_EEPROM_MODAL_SPURS is defined 5. So unless a break occurs, in the
last iteration (i=5) we tried to access spurChansPtr[5] before testing
whether i was within bounds. Fix this.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ar9003_phy.c

@@ -401,7 +401,7 @@ static void ar9003_hw_spur_mitigate_ofdm(struct ath_hw *ah,
 
 	ar9003_hw_spur_ofdm_clear(ah);
 
-	for (i = 0; spurChansPtr[i] && i < 5; i++) {
+	for (i = 0; i < AR_EEPROM_MODAL_SPURS && spurChansPtr[i]; i++) {
 		freq_offset = FBIN2FREQ(spurChansPtr[i], mode) - synth_freq;
 		if (abs(freq_offset) < range) {
 			ar9003_hw_spur_ofdm_work(ah, chan, freq_offset);