scmi: Make transports report the effective length of the received messages

[cristian.marussi_arm.com]

Summary

Once a message is received that fits into the RX buffer, update the
msg.rx_len field with the effective length of the message received.

Tested on: Arm Morello Board
Sponsored by: Arm Ltd
Signed-off-by: Cristian Marussi <[e-mail]>

[andrew]

sys/dev/firmware/arm/scmi_shmem.c

307

This looks wrong, ret is a boolean type so shouldn't be compared with an integer.

[cristian.marussi_arm.com]

sys/dev/firmware/arm/scmi_shmem.c

307

Yes indeed, I will fix.

[cristian.marussi_arm.com]

Fix mishandled retvalue on scmi_shmem_msg_poll and related funcs