package/wayland: install wayland-scanner to $(HOST)

wayland-scanner is needed by weston.

[Peter: use $(INSTALL), fixup white space]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>