rtlwifi: Change REG_CR+2 to MSR

I changed REG_CR+2 and (MSR) to MSR because MSR is defined as (REG_CR + 2).

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>