target: use proper macro for parsing watchpoint address

target: use proper macro for parsing watchpoint address

Currently wp/rwp commands fail on 64-bit targets:

	> wp 0xffffffff80001400 4
	addr option value ('0xffffffff80001400') is not valid

Change-Id: I94d4af906b02b7bd463c8d79a6235a3646dfc434
Signed-off-by: Peter Mamonov <pmamonov@gmail.com>
Reviewed-on: http://openocd.zylin.com/6058
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>