The size of the register cache array is actually 6 instead of 7,
as it caches up to AK4114_REG_INT1_MASK.  This resulted in unexpected
access out of array range, although most of them aren't so serious
(just reading one more byte on the stack at snd_ak4114_create()).

Also, the check of cache size was wrongly done by checking with
sizeof() instead of ARRAY_SIZE().  Fixed this together.

(And yes, hardcoded numbers are bad, but I keep the coding style as is
 for making it clear what this patch actually does.)

Spotted by coverity among several CIDs, e.g. 711621.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>