mfd: rtsx_usb: Fix possible race condition

Fix two possible race condition generated by misuse of del_timer in
rtsx_usb_bulk_transfer_sglist() and uninitialized timers before mfd_add_devices
in rtsx_usb_probe().

Signed-off-by: Roger Tseng <rogerable@realtek.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>