staging: rtl8188eu: Remove redundant CONFIG_88EU_AP_MODE tests

Remove #ifdef's enclosed by an #ifdef test for the same macro to improve
readability.

No code changes:

  md5, CONFIG_88EU_AP_MODE=y:
    b819a33f65133607ebc33b8999ee3a79  r8188eu.o.before
    b819a33f65133607ebc33b8999ee3a79  r8188eu.o.after

  md5, CONFIG_88EU_AP_MODE=n:
    94c84035d59285408b866a57b442276d  r8188eu.o.before
    94c84035d59285408b866a57b442276d  r8188eu.o.after

Signed-off-by: Jakub Sitnicki <jsitnicki@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>