ath9k: Add cast to u8 to FREQ2FBIN macro

The macro results are assigned to u8 variables/fields. Adding the cast
fixes plenty of clang warnings about "implicit conversion from 'int' to
'u8'".
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath9k/eeprom.h

@@ -106,7 +106,7 @@
 #define AR9285_RDEXT_DEFAULT    0x1F
 
 #define ATH9K_POW_SM(_r, _s)	(((_r) & 0x3f) << (_s))
-#define FREQ2FBIN(x, y)		((y) ? ((x) - 2300) : (((x) - 4800) / 5))
+#define FREQ2FBIN(x, y)		(u8)((y) ? ((x) - 2300) : (((x) - 4800) / 5))
 #define FBIN2FREQ(x, y)		((y) ? (2300 + x) : (4800 + 5 * x))
 #define ath9k_hw_use_flash(_ah)	(!(_ah->ah_flags & AH_USE_EEPROM))