ASoC: Intel: avs: Copy only as many RX bytes as necessary

There is no need to copy number of bytes specified by IPC message caller
if DSP firmware returned lower number. In consequence, LARGE_CONFIG_GET
handler is simplified.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20220707124153.1858249-5-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>