dec->reg_cache + 1.
I think it is because CS42L51_FIRSTREG is 0x01,
so codec->reg_cache[0] is not used here.

Then we read CS42L51_NUMREGS bytes to cache.
So we need reg_cache_size to be CS42L51_NUMREGS + 1.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
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