rtl8xxxu: fix RTL8723BU connection failure issue after warm reboot

The RTL8723BU has problems connecting to AP after each warm reboot.
Sometimes it returns no scan result, and in most cases, it fails
the authentication for unknown reason. However, it works totally
fine after cold reboot.

Compare the value of register SYS_CR and SYS_CLK_MAC_CLK_ENABLE
for cold reboot and warm reboot, the registers imply that the MAC
is already powered and thus some procedures are skipped during
driver initialization. Double checked the vendor driver, it reads
the SYS_CR and SYS_CLK_MAC_CLK_ENABLE also but doesn't skip any
during initialization based on them. This commit only tells the
RTL8723BU to do full initialization without checking MAC status.

Signed-off-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>