rpmsg: virtio: Fix possible double free in rpmsg_virtio_add_ctrl_dev()

vch will be free in virtio_rpmsg_release_device() when
rpmsg_ctrldev_register_device() fails. There is no need to call
kfree() again.

Fixes: c486682a ("rpmsg: virtio: Register the rpmsg_char device")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Tested-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220426060536.15594-3-hbh25y@gmail.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>