mmc: sdhci-acpi: fix error return code in sdhci_acpi_add_own_cd()

Fix to return a negative error code in the gpio_to_irq() error
handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>