USB: sl811-hcd: Fix device disconnect

A while ago I provided a patch that fixed device detection after device
removal (USB: sl811-hcd: Fix device disconnect).
Chris Brissette pointed out that the detection/removal counter method
to distinguish insert or remove my fail under certain conditions.
Latest SL811HS datasheet (Document 38-08008 Rev. *D) indicates that
bit 6 (SL11H_INTMASK_RD) of the Interrupt Status Register together with
bit 5 (SL11H_INTMASK_INSRMV) can be used to determine whether a device
has been inserted or removed.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>