sr: fx2lafw: Fix multistage trigger

sr: fx2lafw: Fix multistage trigger

Multistage triggers currently do no work, because there is a return statement
in the middle of the trigger detector which will be hit as soon as the first
stage in a multistage trigger matches. This patch removes the return statement
so that the trigger detector can continue to try to match the next stage. In
order for this to work we also make sure that the trigger stage is only reset
if the current sample does not match.

Signed-off-by: Lars-Peter Clausen <redacted>