scsi: ufs: Remove reset_controller debugfs entry

Debugfs entry reset_controller is designed just for debug purpose and
resetting UFS host through reset_controller may cause stability issues,
hence remove it to avoid misoperation from users.

Change-Id: I64b3c9716ea2763b5752010b5fbd4382027b3e86
Signed-off-by: Can Guo <cang@codeaurora.org>