f2fs: Fix f2fs_truncate_partial_nodes ftrace event

Fix the nid_t field so that its size is correctly reported in the text
format embedded in trace.dat files. As it stands, it is reported as
being of size 4:

        field:nid_t nid[3];     offset:24;      size:4; signed:0;

Instead of 12:

        field:nid_t nid[3];     offset:24;      size:12;        signed:0;

This also fixes the reported offset of subsequent fields so that they
match with the actual struct layout.

Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>