firmware: arm_scmi: Move reinit_completion from scmi_xfer_get to do_xfer

Re-using timed out xfers in a loop can lead to issue if completion was
not properly reinitialized. Move reinit_completion from scmi_xfer_get to
do_xfer to avoid the issue.

Link: https://lore.kernel.org/r/20210606221232.33768-3-cristian.marussi@arm.com


Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
[sudeep.holla: moved reinit_completion instead of adding another one]
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>