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>
(cherry picked from commit 6d1cc3210c)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

kvm-all.c

@@ -1374,14 +1374,12 @@ int kvm_init(void)
     return 0;
 
 err:
-    if (s) {
     if (s->vmfd >= 0) {
         close(s->vmfd);
     }
     if (s->fd != -1) {
         close(s->fd);
     }
-    }
     g_free(s);
 
     return ret;