tracing: Modify saved_tgids size for change in saved_cmdline_size

saved_tgids is fixed size array but uses index upto
savedcmd->cmdline_num. savedcmd->cmdline_num can change
with modification to saved_cmdlines_size node. Fix
this indexing by making saved_tgid part of savedcmd
and modify it's size with changes to saved_cmdline_size.

Change-Id: Ia493f99a3d86d4624414e7605037a1cad35473a9
Signed-off-by: Omprakash Dhyade <odhyade@codeaurora.org>