rtw88: rtw8822c: Remove unused variable 'corr_val'

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/realtek/rtw88/rtw8822c.c: In function ‘rtw8822c_dpk_dc_corr_check’:
 drivers/net/wireless/realtek/rtw88/rtw8822c.c:2445:5: warning: variable ‘corr_val’ set but not used [-Wunused-but-set-variable]

Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201102112410.1049272-39-lee.jones@linaro.org
Link: https://lore.kernel.org/r/20201102112410.1049272-39-lee.jones@linaro.org