screensaver: Fix encoding of ScreenSaverSuspend 'suspend' element

Was using Bool, which is not a defined X protocol encoding type and
has presumably been a 32-bit type. Switch to a CARD32 to be compatible
while at least being well defined.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Mihai Moldovan <ionic@ionic.de>