dwarf-reader: fix undefined behaviour in get_binary_load_address

dwarf-reader: fix undefined behaviour in get_binary_load_address

Within the loop, the call `gelf_getphdr(elf_handle, i, &ph_mem)` is
returning a pointer to `ph_mem` that is only valid in this loop
iteration. The later assignment to *lowest_program_header and its
eventual use to assign load_address leads to undefined behaviour.

	* src/abg-dwarf-reader.cc (get_binary_load_address): Move the
	ph_mem and program_header variables out of the inner for-loop.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>