Fix compiler thinking width and height may be unitialised in frame.c

Fix compiler thinking width and height may be unitialised in frame.c

This fixes the following warning:

	frame.c: In function ‘x_set_frame_parameters’:
	frame.c:3329:25: error: ‘width’ may be used uninitialized in
		this function [-Werror=maybe-uninitialized]
	       adjust_frame_size (f, width_change ? width : -1,
                         ^

* src/frame.c (x_set_frame_parameters): Drop width_changed and
height_changed variables in favour of storing that information in
width and height variables.