ASoC: Stop checking for supplied widgets after we find the first

We don't really care how many widgets a supply is supplying, we just care
if the number is non-zero. This didn't actually produce any improvement
in the test cases I've been using but seems obviously sensible enough that
I'm pushing it out anyway.

We could do a similar thing for other widgets but this may be unhelpful
for further refactorings Liam was working on aiming to allow us to
identify connected audio paths.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>