staging: restore HTC's ram_buffer to fix /proc/last_kmsg

In commit:

commit 203e830df7e962890ab9fcc26e84307abe466e35
Author: Chad Froebel <chad0989@rochester.rr.com>
Date:   Sun May 26 09:14:30 2013 -0400

    Update staging from mako

it changed from using ram_buffer_htc.c to usng ram_buffer.c.
This broke the last_kmsg support.