regmap: cache: Do not fail silently from regcache_sync calls

Call stack of regcache_sync calls may not emit any error message even if
operation was cancelled due an error in I/O driver. One such a silent error
is for instance if I2C bus driver doesn't receive ACK from the I2C device
and returns -EREMOTEIO.

Since many users of regcache_sync() don't check and print the error there is
no any indication that HW registers are potentially out of sync.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>