fbdev: au1200fb: Fix a memory leak in au1200fb_drv_probe()

In au1200fb_drv_probe(), when platform_get_irq fails(), it directly
returns from the function with an error code, which causes a memory
leak.

Replace it with a goto label to ensure proper cleanup.

Fixes: 4e88761f5f8c ("fbdev: au1200fb: Fix missing IRQ check in au1200fb_drv_probe")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>