rpmsg: glink: fix rpmsg device leak

rpmsg: glink: fix rpmsg device leak

While testing rpmsg-char interface it was noticed that duplicate sysfs
entries are getting created and below warning is noticed.

Reason for this is that we are leaking rpmsg device pointer, setting it
null without actually unregistering device.
Any further attempts to unregister fail because rpdev is NULL,
resulting in a leak.

Fix this by unregistering rpmsg device before removing its reference
from rpmsg channel.

sysfs: cannot create duplicate filename '/devices/platform/soc@0/3700000.remot
eproc/remoteproc/remoteproc1/3700000.remoteproc:glink-edge/3700000.remoteproc:
glink-edge.adsp_apps.-1.-1'
[  114.115347] CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not
 tainted 6.16.0-rc4 #7 PREEMPT
[  114.115355] Hardware name: Qualcomm Technologies, Inc. Robotics RB3gen2 (DT)
[  114.115358] Workqueue: events qcom_glink_work
[  114.115371] Call trace:8
[  114.115374]  show_stack+0x18/0x24 (C)
[  114.115382]  dump_stack_lvl+0x60/0x80
[  114.115388]  dump_stack+0x18/0x24
[  114.115393]  sysfs_warn_dup+0x64/0x80
[  114.115402]  sysfs_create_dir_ns+0xf4/0x120
[  114.115409]  kobject_add_internal+0x98/0x260
[  114.115416]  kobject_add+0x9c/0x108
[  114.115421]  device_add+0xc4/0x7a0
[  114.115429]  rpmsg_register_device+0x5c/0xb0
[  114.115434]  qcom_glink_work+0x4bc/0x820
[  114.115438]  process_one_work+0x148/0x284
[  114.115446]  worker_thread+0x2c4/0x3e0
[  114.115452]  kthread+0x12c/0x204
[  114.115457]  ret_from_fork+0x10/0x20
[  114.115464] kobject: kobject_add_internal failed for 3700000.remoteproc:
glink-edge.adsp_apps.-1.-1 with -EEXIST, don't try to register things with
the same name in the same directory.
[  114.250045] rpmsg 3700000.remoteproc:glink-edge.adsp_apps.-1.-1:
device_add failed: -17

Fixes: 835764ddd9af ("rpmsg: glink: Move the common glink protocol implementation to glink_native.c")
Cc: Stable@vger.kernel.org
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250822100043.2604794-2-srinivas.kandagatla@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>