Two comment fixes in gdbtypes.h

This fixes a couple of comments in gdbtypes.h.  One comment had a
typo; and another comment referred to "Moto", which is presumably some
long-gone Motorola-related project.

Tested by rebuilding.

gdb/ChangeLog
2019-05-30  Tom Tromey  <tromey@adacore.com>

	* gdbtypes.h (struct range_bounds) <flag_upper_bound_is_count>:
	Fix comment.
	(TYPE_ARRAY_UPPER_BOUND_IS_UNDEFINED): Rewrite comment.