wcn36xx: Fix error handling path in 'wcn36xx_probe()'

In case of error, 'qcom_wcnss_open_channel()' must be undone by a call to
'rpmsg_destroy_ept()', as already done in the remove function.

Fixes: 5052de8d ("soc: qcom: smd: Transition client drivers from smd to rpmsg")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200507043619.200051-1-christophe.jaillet@wanadoo.fr