Tidy check_uvalue

Tidy check_uvalue

I don't see a need to calculate "ptr = start + uvalue" then compare
"ptr" with "start" and "end".  Given "start <= end" on entry, the
"uvalue" comparison with "max_uvalue" ought to be sufficient to ensure
"start + uvalue" is bounded by "start" and "end" regardless of the
size of pointers and the unsigned dwarf_vma integer type.

	* dwarf.c (check_uvalue): Remove unnecessary pointer checks.