staging: rtl8188eu: write out multiplying in wifirate2_ratetbl_inx()

Write out multiplying in wifirate2_ratetbl_inx() to improve
readabilitiy and clear checkpatch issues with missing spaces
around '*' operator.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>