cpu: Make comparing PowerPC CPUs easier to read

Revert the condition to make it easier to read. The function is also
renamed as ppcCompare to match other functions in PowerPC CPU driver.

src/cpu/cpu_powerpc.c

@@ -414,15 +414,14 @@ no_memory:
 }
 
 static virCPUCompareResult
-PowerPCCompare(virCPUDefPtr host,
+ppcCompare(virCPUDefPtr host,
            virCPUDefPtr cpu)
 {
-    if ((cpu->arch != VIR_ARCH_NONE &&
-         (host->arch != cpu->arch)) ||
-        STRNEQ(host->model, cpu->model))
-        return VIR_CPU_COMPARE_INCOMPATIBLE;
+    if ((cpu->arch == VIR_ARCH_NONE || host->arch == cpu->arch) &&
+        STREQ(host->model, cpu->model))
+        return VIR_CPU_COMPARE_IDENTICAL;
 
-    return VIR_CPU_COMPARE_IDENTICAL;
+    return VIR_CPU_COMPARE_INCOMPATIBLE;
 }
 
 static int
@@ -631,7 +630,7 @@ struct cpuArchDriver cpuDriverPowerPC = {
     .name = "ppc64",
     .arch = archs,
     .narch = ARRAY_CARDINALITY(archs),
-    .compare    = PowerPCCompare,
+    .compare    = ppcCompare,
     .decode     = PowerPCDecode,
     .encode     = NULL,
     .free       = PowerPCDataFree,