xl: initialise rc before using it in vcpuset

In 5b725e56 (xl: improve return and exit codes of vcpu related
functions), the return value of libxl_cpu_bitmap_alloc was not stored in
rc anymore. Yet the subsequent fprintf still used that.

Reinstate the original implementation, that is, to store return value of
libxl_cpu_bitmap_alloc in rc before using rc.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/xl_cmdimpl.c

@@ -5473,7 +5473,8 @@ static int vcpuset(uint32_t domid, const char* nr_vcpus, int check_host)
         if (rc)
             return 1;
     }
-    if (libxl_cpu_bitmap_alloc(ctx, &cpumap, max_vcpus)) {
+    rc = libxl_cpu_bitmap_alloc(ctx, &cpumap, max_vcpus);
+    if (rc) {
         fprintf(stderr, "libxl_cpu_bitmap_alloc failed, rc: %d\n", rc);
         return 1;
     }