LU-6142 llite: use %pd to report dentry names.

Since Linux 3.12, it has been possible use the "%pd" format specifier
to print a dentry name, so use that instead of "%.*s" and having
to pass both the length and the name.

Redhat's 3.10 kernels also have this functionality backported.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I70303a2c375d54825e89a0ba6703914528c54c05
Reviewed-on: https://review.whamcloud.com/38442
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>