staging: rtl8188eu: Fix static symbol sparse warnings

Fix sparse warnings:
drivers/staging/rtl8188eu/core/rtw_cmd.c:52:5: warning:
  symbol '_rtw_enqueue_cmd' was not declared. Should it be static?
drivers/staging/rtl8188eu/core/rtw_wlan_util.c:1225:5: warning:
  symbol 'wifirate2_ratetbl_inx' was not declared. Should it be static?
drivers/staging/rtl8188eu/hal/HalPhyRf_8188e.c:25:4: warning:
  symbol 'ODM_GetRightChnlPlaceforIQK' was not declared. Should it be static?
drivers/staging/rtl8188eu/os_dep/ioctl_linux.c:3109:5: warning:
  symbol 'rtw_ioctl' was not declared. Should it be static?

Signed-off-by: Jeff Oczek <jeffoczek@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>