drm/panthor: Fix error code in panthor_gpu_init()

This code accidentally returns zero/success on error because of a typo.
It should be "irq" instead of "ret".  The other thing is that if
platform_get_irq_byname() were to return zero then the error code would
be cmplicated.  Fortunately, it does not so we can just change <= to
< 0.

Fixes: 5cd894e2 ("drm/panthor: Add the GPU logical block")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d753e684-43ee-45c2-a1fd-86222da204e1@moroto.mountain