ASoC: let snd_soc_update_bits() return an error code

Update snd_soc_update_bits() so that it returns a negative error code if the
the read or write operation fails.

Note that currently, a lot of the lower-level read functions have an unsigned
integer return type (and some of them even try to return a negative number),
but this code still appears to work in those cases.

An examination of the code shows that all current callers are compatible with
this change.

Signed-off-by: Timur Tabi <timur@freescale.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>