rtw88: 8723d: fix incorrect setting of ldo_pwr

Currently ldo_pwr has the LDO25 voltage bits set to zero and then
it is overwritten with the new voltage setting. The assignment
looks incorrect, it should be bit-wise or'ing in the new voltage
setting rather than a direct assignment.

Addresses-Coverity: ("Unused value")
Fixes: 1afb5eb7

 ("rtw88: 8723d: Add cfg_ldo25 to control LDO25")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200514181329.16292-1-colin.king@canonical.com