Fix: flt.lttng-utils.debug-info: memory leak

Fix: flt.lttng-utils.debug-info: memory leak

The gelf_getshdr() function return a pointer to the second parameter on
success and NULL on error. This means that on we overwrite the
`curr_section_hdr` variable and leak memory.

To fix it, we simply change the variable from a heap allocated variable
to a stack allocated variable this has the effect of making code simpler.

Found using scan-build:
  line 334, column 7
  Potential leak of memory pointed to by 'curr_section_hdr'

Report-by: scan-build (ad8e62)
Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I5cc4049075e4ca1d64d98e17662f935e6562bb6e
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1265
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>