rtc: max77686: Use ffs() to calculate tm_wday

max77686_rtc_calculate_wday() is used to calculate the day of the week
to be filled in struct rtc_time but that function only calculates the
number of bits shifted.  So the ffs() function can be used to find the
first bit set instead of a special function.

[akpm@linux-foundation.org: add comment clarifying ffs() use]
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-max77686.c

@@ -70,16 +70,6 @@ enum MAX77686_RTC_OP {
 	MAX77686_RTC_READ,
 };
 
-static inline int max77686_rtc_calculate_wday(u8 shifted)
-{
-	int counter = -1;
-	while (shifted) {
-		shifted >>= 1;
-		counter++;
-	}
-	return counter;
-}
-
 static void max77686_rtc_data_to_tm(u8 *data, struct rtc_time *tm,
 				   int rtc_24hr_mode)
 {
@@ -93,7 +83,8 @@ static void max77686_rtc_data_to_tm(u8 *data, struct rtc_time *tm,
 			tm->tm_hour += 12;
 	}
 
-	tm->tm_wday = max77686_rtc_calculate_wday(data[RTC_WEEKDAY] & 0x7f);
+	/* Only a single bit is set in data[], so fls() would be equivalent */
+	tm->tm_wday = ffs(data[RTC_WEEKDAY] & 0x7f) - 1;
 	tm->tm_mday = data[RTC_DATE] & 0x1f;
 	tm->tm_mon = (data[RTC_MONTH] & 0x0f) - 1;
 	tm->tm_year = (data[RTC_YEAR] & 0x7f) + 100;