remoteproc: qcom: q6v5: Fix potential null-ptr-deref in q6v5_wcss_init_mmio()

q6v5_wcss_init_mmio() will call platform_get_resource_byname() that may
fail and return NULL. devm_ioremap() will use res->start as input, which
may causes null-ptr-deref. Check the ret value of
platform_get_resource_byname() to avoid the null-ptr-deref.

Fixes: 0af65b9b ("remoteproc: qcom: wcss: Add non pas wcss Q6 support for QCS404")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221125021641.29392-1-shangxiaojing@huawei.com