pstore: Remove "-0" suffix from console-ramoops

The Android framework expects last kmsg to be located at
/sys/fs/pstore/console-ramoops when it collects crash metrics,
so remove the "-%lld" suffix to maintain compatibility.
Based on commit 0fb78957ffe0447a1072ec307ce342e5437c0791
("pstore: use scnprintf") from the Marlin tree.

Bug: 36231027
Change-Id: I3670edb12113b6962ad225ee56c48e1894171dab
Signed-off-by: Siqi Lin <siqilin@google.com>