rpmsg: Fix rpmsg_create_ept return when RPMSG config is not defined

stable inclusion
from stable-5.10.80
commit 602ab1fd40e2c5cb8d3664379da967528833844c
bugzilla: 185821 https://gitee.com/openeuler/kernel/issues/I4L7CG

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=602ab1fd40e2c5cb8d3664379da967528833844c



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[ Upstream commit 537d3af1 ]

According to the description of the rpmsg_create_ept in rpmsg_core.c
the function should return NULL on error.

Fixes: 2c8a5708 ("rpmsg: Provide function stubs for API")
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20210712123912.10672-1-arnaud.pouliquen@foss.st.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Reviewed-by: Weilong Chen <chenweilong@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>