Use field_core_addr in more places

Use field_core_addr in more places

This changes a few spots that use field_fmt to use field_core_addr
instead.

gdb/ChangeLog
2019-07-15  Tom Tromey  <tromey@adacore.com>

	* target.c (flash_erase_command): Use field_core_addr.
	* symfile.c (generic_load): Use field_core_addr.
	* sparc64-linux-tdep.c (sparc64_linux_handle_segmentation_fault):
	Use field_core_addr.
	* i386-linux-tdep.c (i386_linux_handle_segmentation_fault): Use
	field_core_addr.