i965: report bound buffer size not underlying buffer size for image size (v2)

i965: report bound buffer size not underlying buffer size for image size (v2)

This seems to make sense, the image is bound to a subset of the buffer
so the image size should be from the bound size not the underlying
object.

This fixes:
GL44-CTS.shader_image_size.advanced-nonMS-fs-int

v2: get mininum of the two values, same as we write to the hw.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>