mips: mt76x8: ddr_cal: Correct dqs_find_min/max implementations

The current implementations have some issues detecting the correct
values:

dqs_find_max() will return "last passing fieldval + 1" instead of
"last passing fieldval". Also it will return "maxval + 1" in the
case that all fieldvals are tested valid (without error).

dqs_find_min() will not test the "lowest" value because of using ">"
instead of ">=".

This patch now rewrites these functions to fix those issues. Also,
this patch uses the same approach of a for loop in both functions making
it easier to read and maintain.

Since the variables are integers now, we can use min()/max(), which
handles the wrap around case for fieldval=0: return (0 - 1).

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Weijie Gao <weijie.gao@mediatek.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Weijie Gao <weijie.gao@mediatek.com>

arch/mips/mach-mtmips/ddr_cal.c

@@ -74,39 +74,31 @@ static inline bool dqs_test_error(void __iomem *memc, u32 memsize, u32 dqsval,
 static inline int dqs_find_max(void __iomem *memc, u32 memsize, int initval,
 			       int maxval, int shift, u32 regval)
 {
-	int fieldval = initval;
+	int fieldval;
 	u32 dqsval;
 
-	do {
+	for (fieldval = initval; fieldval <= maxval; fieldval++) {
 		dqsval = regval | (fieldval << shift);
-
 		if (dqs_test_error(memc, memsize, dqsval, 3))
-			break;
-
-		fieldval++;
-	} while (fieldval <= maxval);
+			return max(fieldval - 1, initval);
+	}
 
-	return fieldval;
+	return maxval;
 }
 
 static inline int dqs_find_min(void __iomem *memc, u32 memsize, int initval,
 			       int minval, int shift, u32 regval)
 {
-	int fieldval = initval;
+	int fieldval;
 	u32 dqsval;
 
-	while (fieldval > minval) {
+	for (fieldval = initval; fieldval >= minval; fieldval--) {
 		dqsval = regval | (fieldval << shift);
-
-		if (dqs_test_error(memc, memsize, dqsval, 1)) {
-			fieldval++;
-			break;
-		}
-
-		fieldval--;
+		if (dqs_test_error(memc, memsize, dqsval, 1))
+			return min(fieldval + 1, initval);
 	}
 
-	return fieldval;
+	return minval;
 }
 
 void ddr_calibrate(void __iomem *memc, u32 memsize, u32 bw)