rpmsg: qcom_smd: Fix returning 0 if irq_of_parse_and_map() fails

irq_of_parse_and_map() returns 0 on failure, so this should not be
passed further as error return code.

Fixes: 1a358d35 ("rpmsg: qcom_smd: Fix irq_of_parse_and_map() return value")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220423093932.32136-1-krzysztof.kozlowski@linaro.org