mfd: rtsx: Clear hardware PFM mode in rtl8411b

Clear hw_pfm_en to disable hardware PFM mode, to fix a bug that in some
situation registers in 0xFDxx domain can't be accessed.

Signed-off-by: Wei WANG <wei_wang@realsil.com.cn>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>