You need the `rtl8188efw.bin` firmware file to be somewhere in `/lib/firmware`.
If it isn't packaged for Centos 6.7, you can get it (along with a lot of other firmware) with:
git clone git://git.kernel.org/pub/scm/linux/kernel/git/dwmw2/linux-firmware.git
Then copy it into `/lib/firmware/`
BTW, on my debian system, it is in the `firmware-realtek` package with filename `/lib/firmware/rtlwifi/rtl8188efw.bin`
If it isn't being automatically loaded at boot time (it should be), you also need to ensure that the `rtl8188ee` kernel module is being loaded.