libelf/elf_newscn.c: fix build failure against gcc-14 (-Walloc-size)

libelf/elf_newscn.c: fix build failure against gcc-14 (-Walloc-size)

`gcc-14` adde a new -Walloc-size warning that makes sure that size of an
individual element matches size of a pointed type:

    https://gcc.gnu.org/PR71219

`elfutils` triggers is on `calloc()` call where member size is sued as
`1`.

    elf_newscn.c: In function `elf_newscn`:
    elf_newscn.c:97:12: error: allocation of insufficient size «1» for type «Elf_ScnList» with size «16» [-Werror=alloc-size]
       97 |       newp = calloc (sizeof (Elf_ScnList)
          |            ^

The change swaps arguments to pass larger value as a member size.

Signed-off-by: Sergei Trofimovich <slyich@gmail.com>