staging: greybus: audio_codec.h: Prefer kernel type 'u32' over 'uint32_t'

Fix the following errors found by checkpatch.pl:
CHECK: Prefer kernel type 'u32' over 'uint32_t'

Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>