This chipset is not supported by all images, you should first search if it's supported and available in the feeds.

Code:
opkg update
opkg list | grep rtl8188eu
opkg list_installed | grep rtl8188eu


TS
_________________________
DM8000, DM800se, DM500HD, DM800HD, DM7025, DM7020s, DM7000, DM500s
VU+ Solo, VU+ Uno, VU+ Duo, Kathrein UFS910
Tivusat, TNTSat, Fransat, SSR/TSR, BBC1-2-3/ITV
DE-OpenBlackHole 1.4 image : http://www.openblackhole.com/