cypress_m8: Feature buffer fixes

From: Mike Isely <isely@pobox.com>

Don't hardcode the feature buffer size; use sizeof() instead.  That
way we can easily specify the size in a single spot.  Speaking of the
feature buffer size, the Cypress app note (and further testing with a
DeLorme Earthmate) suggests that this size should be 5 not 8 bytes.
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>