staging: r8188eu: refactor rtw_ch2freq()

Convert the array ch_freq_map to a simple integer array and use
the indices as channel numbers. This simplifies the code and avoids
looping through the array to get the frequency. To avoid out of
bounds array access return a default value for invalid channel values,
like the original code did.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20220222082847.6687-3-straube.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/core/rtw_rf.c

@@ -8,32 +8,27 @@
 #include "../include/recv_osdep.h"
 #include "../include/xmit_osdep.h"
 
-struct ch_freq {
-	u32 channel;
-	u32 frequency;
+static const u32 ch_freq_map[] = {
+	2412,
+	2417,
+	2422,
+	2427,
+	2432,
+	2437,
+	2442,
+	2447,
+	2452,
+	2457,
+	2462,
+	2467,
+	2472,
+	2484
 };
 
-static struct ch_freq ch_freq_map[] = {
-	{1, 2412}, {2, 2417}, {3, 2422}, {4, 2427}, {5, 2432},
-	{6, 2437}, {7, 2442}, {8, 2447}, {9, 2452}, {10, 2457},
-	{11, 2462}, {12, 2467}, {13, 2472}, {14, 2484},
-};
-
-static int ch_freq_map_num = ARRAY_SIZE(ch_freq_map);
-
 u32 rtw_ch2freq(u32 channel)
 {
-	u8	i;
-	u32	freq = 0;
-
-	for (i = 0; i < ch_freq_map_num; i++) {
-		if (channel == ch_freq_map[i].channel) {
-			freq = ch_freq_map[i].frequency;
-				break;
-		}
-	}
-	if (i == ch_freq_map_num)
-		freq = 2412;
+	if (channel == 0 || channel > ARRAY_SIZE(ch_freq_map))
+		return 2412;
 
-	return freq;
+	return ch_freq_map[channel - 1];
 }