write_pieced_value: Fix buffer offset for memory pieces

write_pieced_value: Fix buffer offset for memory pieces

In write_pieced_value, when transferring the data to target memory via a
buffer, the bit offset within the target value is not reduced to its
sub-byte fraction before using it as a bit offset into the buffer.  This
is fixed.

gdb/ChangeLog:

	* dwarf2loc.c (write_pieced_value): In DWARF_VALUE_MEMORY,
	truncate full bytes from dest_offset_bits before using it as an
	offset into the buffer.