staging: rtl8192e: Refactor tmp_ofdm_index variable assignment

Refactor tmp_ofdm_index variable assignment to avoid multiple
assignments which is not accepted by checkpatch.

Signed-off-by: Yogesh Hegde <yogi.kernel@gmail.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/af7bc22ec142c33cf7346c1ab13d192b55095d1e.1683730854.git.yogi.kernel@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>