lowmem: remove an unecessary local variable

This "changed" variable is kind of deprecated. We used to have a spinlock
[which was later deemed unecessary] around the first if clause in the
*_watermark_state() functions; the variable was needed in order to move the
operation in the second if clause out of the lock section.

Signed-off-by: Viktor Rosendahl <viktor.rosendahl@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>