linux-user/elfload.c: Avoid calling g_free() on uninitialized data

Avoid calling g_free() on unintialized data in the error-handling
paths in elf_core_dump() by splitting the initialization of the
elf_note_info struct out of fill_note_info() so that it's always
valid to call free_note_info() whether we got to the point of
being able to fill_note_info() or not.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
