rpmsg: qcom_smd: Fix redundant channel->registered assignment

In qcom_channel_state_worker(), we are setting channel->registered
to true when registering a channel, but this is getting repeated both
before and after re-locking the channels_lock spinlock, which is
obviously a typo.
Remove the assignment done out of the spinlock to fix this redundancy.

Fixes: 53e2822e

 ("rpmsg: Introduce Qualcomm SMD backend")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220114133259.247726-1-angelogioacchino.delregno@collabora.com