LU-6210 ldlm: Change positional struct initializers to C99

This patch makes no functional changes.  Struct initializers in the
ldlm directory that use C89 or GCC-only syntax are updated to C99
syntax.

The C99 syntax prevents incorrect initialization if values are
accidently placed in the wrong position, allows changes in the struct
definition, and clears any members that are not given an explicit
value.

The following struct initializers have been updated:

lustre/ldlm/ldlm_extent.c:
	struct interval_node_extent limiter
	struct interval_node_extent ext

Test-Parameters: trivial
Signed-off-by: Steve Guminski <stephenx.guminski@intel.com>
Change-Id: I219f5b2bd4b96d92eaf120f7080e762d72eb3105
Reviewed-on: https://review.whamcloud.com/23743
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>