rtlwifi: rtl8192cu: Fix duplicate if test

A typo causes routine rtl92cu_phy_rf6052_set_cck_txpower() to test the
same condition twice. The problem was found using cppcheck-1.49, and the
proper fix was verified against the pre-mac80211 version of the code.

This patch was originally included as commit 1288aa4e, but was accidentally
reverted in a later patch.

Reported-by: David Binderman <dcb314@hotmail.com> [original report]
Reported-by: Andrea Morello <andrea.merello@gmail.com> [report of accidental reversion]
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: stable <stable@vger.kernel.org>  [back to 2.6.39]
Signed-off-by: John W. Linville <linville@tuxdriver.com>