ASoC: cs42xx8: Move the code checking *regmap argument earlier

Slightly improve the readability by moving the code checking *regmap
argument earlier. Also move the assignment of of_id close to the place
testing it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>