rtlwifi: rtl8188ee: Fix warning when building on big-endian systems

In http://lkml.indiana.edu/hypermail/linux/kernel/1305.1/index.html

,
Geert Uytterhoeven reports a new warning when building 3.10-rc1 in
this driver. This is caused by using a "#if" test to see if __LITTLE_ENDIAN
is set, which fails for all big-endian systems. Change to "ifdef".

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>