perf record: Fix filemap pathname parsing in /proc/pid/maps

perf record: Fix filemap pathname parsing in /proc/pid/maps

Looking backward for the first space from the end of a line in
/proc/pid/maps does not find the start of the pathname of the mapped
file if it contains a space.

Since the only slashes we have in this file occur in the (absolute!)
pathname column of file mappings, looking for the first slash in a
line is a safe method to find the name.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Stefani Seibold <stefani@seibold.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090624190835.GA25548@cmpxchg.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>