ASoC: cs4271: fix property check

The driver had the property check for 'cirrus,amutec_eq_bmutec' the
wrong way around. That happens if you misspell the property in the
bindings during tests.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>