greybus: greybus_protocols.h: convert __u32 to __le32

greybus: greybus_protocols.h: convert __u32 to __le32

All 32 bit declarations associated with data interchange to the greybus
network need to be declared explicitly as little-endian since that is the
byte order we use on the greybus network. struct gb_audio_topology is
declaring its variables as u32. Fortunately this structure isn't currently
used so we can do a conversion from u32 to __le32 without any ancillary
code-churn.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>