rtlwifi: rtl8192cu: Remove variable self-assignment in rf.c

In _rtl92c_get_txpower_writeval_by_regulatory() the variable writeVal
is assigned to itself in an if ... else statement, apparently only to
document that the branch condition is handled and that a previously read
value should be returned unmodified. The self-assignment causes clang to
raise the following warning:

drivers/net/wireless/realtek/rtlwifi/rtl8192cu/rf.c:304:13:
  error: explicitly assigning value of variable of type 'u32'
    (aka 'unsigned int') to itself [-Werror,-Wself-assign]
  writeVal = writeVal;

Delete the branch with the self-assignment.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>