fbdev: goldfishfb: Do not check 0 for platform_get_irq()

Since platform_get_irq() never returned zero, so it need not to check
whether it returned zero, and we use the return error code of
platform_get_irq() to replace the current return error code.

Please refer to the commit a85a6c86 ("driver core: platform: Clarify
that IRQ 0 is invalid") to get that platform_get_irq() never returned
zero.

Signed-off-by: Zhu Wang <wangzhu9@huawei.com>
Signed-off-by: Helge Deller <deller@gmx.de>