wifi: rtl8xxxu: Fix assignment to bit field priv->pi_enabled

Just because priv->pi_enabled is only one bit doesn't mean it works
like a bool. The value assigned to it loses all bits except bit 0,
so only assign 0 or 1 to it.

This affects the RTL8188FU, but fixing the assignment didn't make
a difference for my device.

Fixes: c888183b

 ("wifi: rtl8xxxu: Support new chip RTL8188FU")
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/4368d585-11ec-d3c7-ec12-7f0afdcedfda@gmail.com