trace: Fix array index out of bounds violation

The trace sequence buffer max is only PAGE_SIZE, make sure the
length is validated before accessing the array.

Change-Id: I65848257fc4249def83fe68bb2dba1c6e73b841d
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>