rtlwifi: rtl8192se: Fix wrong assignment

There is a typo in the struct member name on assignment when checking
rtlphy->current_chan_bw == HT_CHANNEL_WIDTH_20_40, the check uses pwrgroup_ht40
for bound limit and uses pwrgroup_ht20 when assigning instead.

Signed-off-by: Felipe Pena <felipensp@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable@vger.kernel.org [3.0+]
Signed-off-by: John W. Linville <linville@tuxdriver.com>