scripts/namespace.pl: fix wrong source path

File::Find will do chdir automatically, so we need to get the absolute
patch with $File::Find::dir.

Reported-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Amerigo Wang <amwang@redhat.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>