codegen: Drop useless temp variable when creating structs
codegen: Drop useless temp variable when creating structs

Partially fixes 657378.

jessevdk/vala,GNOME/vala,flobrosch/vala-fixes,GNOME/vala,severinh/vala,Distrotech/vala,Distrotech/vala,xdave/pvala,flobrosch/vala-fixes,kamanashisroy/aroop,frida/vala,flobrosch/vala-fixes,playya/vala,tjol/vala-tjol,spidermonkdust/vala,rvu95/vala,GNOME/vala,kamanashisroy/aroop,tjol/vala-tjol,frida/vala,frida/vala,severinh/vala,playya/vala,tjol/vala-tjol,Distrotech/vala,frida/vala,rvu95/vala,spidermonkdust/vala,frida/vala,spidermonkdust/vala,rvu95/vala,jessevdk/vala,GNOME/vala,kamanashisroy/aroop,severinh/vala,playya/vala,jessevdk/vala