codegen: Don't check for comma expression in get_field_cvalue
codegen: Don't check for comma expression in get_field_cvalue

All comma expressions have been dropped, so it's not possible that
an inner C expression is a comma expression.

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