LU-8066 ldlm: match store macro prototype

LU-8066 ldlm: match store macro prototype

Use size_t in the LDLM_POOL_SYSFS_WRITER_STORE() function declaration
to match the struct lustre_attr (*store) function prototype.

Test-Paramters: trivial
Fixes: 1196bd199e7 ("LU-8066 ldlm: move /proc/fs/lustre/ldlm to /sys")

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I41012a66507a048c63bfe6b6e732cf858ba5a5b1
Reviewed-on: https://review.whamcloud.com/33920
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>