coresight: byte-cntr: fix the bufp intialisation

When the ETR is disabled and receiver application is
still reading, if the IRQ count of byte-cntr is not
zero, then the expected unread data is to be pushed
to the receiver end. The buffer pointer of ETR DDR
is to be intialised to read the data.

Change-Id: I288f129354e85228d3ac4acc749bb000c6aaf014
Signed-off-by: Saranya Chidura <schidura@codeaurora.org>