runstate: Initialize Error * to NULL

runstate: Initialize Error * to NULL

Based on the description of error_setg(), the local variable err in
qemu_init_subsystems() should be initialized to NULL.

Fixes: efd7ab22fb ("vl: extract qemu_init_subsystems")
Cc: qemu-stable@nongnu.org
Signed-off-by: Peng Liang <liangpeng10@huawei.com>
Message-Id: <20210610131729.3906565-1-liangpeng10@huawei.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 6e1da3d305499d3907f3c7f6638243e2e09b5085)
Signed-off-by: Michael Roth <michael.roth@amd.com>