dma-buf: align debugfs output

Align the heading with the values output from debugfs.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/E1cttOq-0006GX-U7@rmk-PC.armlinux.org.uk