kvm: Fix warning from static code analysis

Report from smatch:

kvm-all.c:1373 kvm_init(135) warn:
 variable dereferenced before check 's' (see line 1360)

's' cannot by NULL (it was alloced using g_malloc0), so there is no need
to check it here.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

kvm-all.c

@@ -1409,13 +1409,11 @@ int kvm_init(void)
     return 0;
 
 err:
-    if (s) {
-        if (s->vmfd >= 0) {
-            close(s->vmfd);
-        }
-        if (s->fd != -1) {
-            close(s->fd);
-        }
+    if (s->vmfd >= 0) {
+        close(s->vmfd);
+    }
+    if (s->fd != -1) {
+        close(s->fd);
     }
     g_free(s);