tests: Fix compilation error
tests: Fix compilation error

Fix compilation error due to -Werror=maybe-uninitialized:

  CC       test-display-base.o
test-display-base.c: In function 'do_wakeup':
test-display-base.c:579:13: error: 'update' may be used uninitialized...
             push_command(&update->ext);

Signed-off-by: Snir Sheriber <a22152bc672d3e177f23883338efc60c231ec881@redhat.com>
Acked-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>

fgouget/spice,fgouget/spice,fgouget/spice,fgouget/spice