powerpc/xmon: use match_string() helper

match_string() returns the index of an array for a matching string,
which can be used instead of open coded variant.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/xmon/xmon.c

@@ -3173,7 +3173,7 @@ skipbl(void)
 }
 
 #define N_PTREGS	44
-static char *regnames[N_PTREGS] = {
+static const char *regnames[N_PTREGS] = {
 	"r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7",
 	"r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15",
 	"r16", "r17", "r18", "r19", "r20", "r21", "r22", "r23",
@@ -3208,18 +3208,17 @@ scanhex(unsigned long *vp)
 			regname[i] = c;
 		}
 		regname[i] = 0;
-		for (i = 0; i < N_PTREGS; ++i) {
-			if (strcmp(regnames[i], regname) == 0) {
-				if (xmon_regs == NULL) {
-					printf("regs not available\n");
-					return 0;
-				}
-				*vp = ((unsigned long *)xmon_regs)[i];
-				return 1;
-			}
+		i = match_string(regnames, N_PTREGS, regname);
+		if (i < 0) {
+			printf("invalid register name '%%%s'\n", regname);
+			return 0;
 		}
-		printf("invalid register name '%%%s'\n", regname);
-		return 0;
+		if (xmon_regs == NULL) {
+			printf("regs not available\n");
+			return 0;
+		}
+		*vp = ((unsigned long *)xmon_regs)[i];
+		return 1;
 	}
 
 	/* skip leading "0x" if any */