return error for unsupported bits-per-word format, BUG() is not right
for this scenerios as we are not an ASSERT but an error handler.
Signed-off-by: NQipan Li <Qipan.Li@csr.com>
Signed-off-by: NBarry Song <baohua.song@csr.com>
Signed-off-by: NMark Brown <broonie@kernel.org>