axfer: Fix creation of v1.2 headers on big-endian systems

axfer: Fix creation of v1.2 headers on big-endian systems

struct block_v120_format defines these members as uint8_t. On
little-endian systems, no swapping is done, and the generated block
header is fine. However, on big-endian machines, the value is swapped to
the high byte and then truncated by the assignment, causing both
bits_per_sample and samples_per_frame to be zero.

This fixes an assertion failure in container-test when later
parsing the header ["assert(*samples_per_frame > 0);" in
container_context_pre_process()].

Fixes: 4ab7510f3a18: ("axfer: add support for a container of Creative Tech. voice format")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>