clipboard: set fd member of clipboard_source
clipboard: set fd member of clipboard_source

The fd member of clipboard_source structure was not set
but was used in close().

v2. don't do unnecessary changes

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>
Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

kwm81/weston,Gnurou/weston,jonnylamb/weston,eyolfson/weston,sir-murray/weston,sir-murray/weston,kwm81/weston,krezovic/weston,Tarnyko/weston-xdg_surface_present,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,Gnurou/weston,udoprog/weston,Fantu/compositor-spice,udoprog/weston,giucam/weston,xorgy/weston,giucam/weston,mchalupa/weston,eyolfson/weston,krezovic/weston,Fantu/compositor-spice,xorgy/weston,jonnylamb/weston,mchalupa/weston