drm/kmb: Fix error return code in kmb_hw_init()

When the call to platform_get_irq() to obtain the IRQ of the lcd fails, the
returned error code should be propagated. However, we currently do not
explicitly assign this error code to 'ret'. As a result, 0 was incorrectly
returned.

Fixes: 7f7b96a8 ("drm/kmb: Add support for KeemBay Display")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210513134639.6541-1-thunder.leizhen@huawei.com