Remove declarations from m32c-tdep.c

Remove declarations from m32c-tdep.c

This removes some unused declarations from m32c-tdep.c.  Initially I
had thought that this entire code block was dead, but Simon pointed
out that it is not; so this patch simply removes some declarations.

gdb/ChangeLog
2018-07-22  Tom Tromey  <tom@tromey.com>

	* m32c-tdep.c (mark_dma): Return void.
	(make_regs): Remove unused declarations.