rpmsg: qcom_smd: Fix irq_of_parse_and_map() return value

The irq_of_parse_and_map() returns 0 on failure, not a negative ERRNO.

Fixes: 53e2822e ("rpmsg: Introduce Qualcomm SMD backend")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220422105326.78713-1-krzysztof.kozlowski@linaro.org