firmware: arm_scmi: Avoid multiple initialisations of hdr->protocol_id

firmware: arm_scmi: Avoid multiple initialisations of hdr->protocol_id

Since the hdr->protocol_id is set from the scmi_protocol_instance handle
just before the transfer, there is no need to initialise the same in
scmi_xfer_get_init. Remove the unnecessary initialisations.

Link: https://lore.kernel.org/r/20210608140140.2042257-1-sudeep.holla@arm.com
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>