cypress_m8: use appropriate URB polling interval

The polling interval for the device can't always be 1msec.  If it is
too quick, the device can fail causing a fatal (to the driver) EILSEQ
error from the USB core.  The actual correct value is reported by the
device as part of its configuration data, so use that value as the
default.  On a DeLorme Earthmate for example, the device reports that
it wants a 6msec interval.  As part of this fix, the "interval" module
option has been fixed as well; the device's default can be overridden
by specifying interval=<value> as a module option.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>