Use the existing SBUILD_ID_SIZE macro instead of the equivalent
BUILD_ID_SIZE * 2 + 1 expression for allocating a buffer for build-id
strings.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Hemant Kumar <hemant@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20160511135159.23943.57120.stgit@devbox


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>