buildroot

package/linuxptp: fix coding style issue

Thanks to Yann for the live review during the Buildroot summer camp.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Petr Kulhavy <brain@jikos.cz>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>