capped: fix handling of assignments

capped: fix handling of assignments

The problem that this change tries to address is:

	if (x > foo)
		return;
	// x is now capped
	if (x < 0)
		x = 0;  // <- this assignement makes it uncapped

When we're handling this assignment the modification hook first sets it
to uncapped.  Then this assignment can set things back to capped.  The
!is_capped() condition makes no sense, because it won't be capped.

If it's a += assignment then that's uncapped.  If the right hand side is
capped then it's capped.  If we had a state and we're setting it to a
partial range then set it to capped.  (If we don't have a state then forget
about it).

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>