rtw88: pci: use for loop instead of while loop for DBI/MDIO

Use a for loop to polling DBI/MDIO read/write flags to avoid
infinite loop happens

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Reviewed-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>