MicroBlaze: Widen mask used in opcodes/microblaze-dis,c

Instead of using 0xFFFF0000, or with (~0xFFFF) to sign extend
negative 16-bit value and with (~0xFFFF) to extract higher order
address bits

opcodes/
	* microblaze-dis.c: (print_insn_microblaze): Widen mask
	(microblaze_get_target_address): Likewis

Signed-off-by: Gopi Kumar Bulusu <gopi@sankhya.com>
Signed-off-by: Michael J. Eager <eager@eagercon.com>