ubsan: h8300: left shift cannot be represented in type 'int'

ubsan: h8300: left shift cannot be represented in type 'int'

This is
  *cst = (data[0] << 24) + (data[1] << 16) + (data[2] << 8) + data[3];
data is unsigned char which promotes to int.

	* h8300-dis.c (extract_immediate): Avoid signed overflow.
	(bfd_h8_disassemble): Likewise.