qga: fix file descriptor leak

The file descriptor for /sys/power/state was never closed.  Reported
by Coverity.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-posix.c

@@ -1652,6 +1652,7 @@ static bool linux_sys_state_supports_mode(SuspendMode mode, Error **errp)
     }
 
     ret = read(fd, buf, sizeof(buf) - 1);
+    close(fd);
     if (ret <= 0) {
         return false;
     }