[PATCH] sata_sil24: update sil24_hardreset()

Use phy debouncing instead of unconditional wait after DEV_RST and
make sil24_hardreset() to request followup SRST as that's the only way
to wait for !BSY.  Note that the original implementation never worked
- if the cached status was !BSY, ata_busy_sleep() finished
immediately; otherwise, it timed out regardless of the actual device
status.

Signed-off-by: Tejun Heo <htejun@gmail.com>