drm/panthor: Preserve the result returned by panthor_fw_resume()

drm/panthor: Preserve the result returned by panthor_fw_resume()

WARN() will return true if the condition is true, false otherwise.
If we store the return of drm_WARN_ON() in ret, we lose the actual
error code.

v3:
- Add R-b
v2:
- Add R-b

Fixes: 5fe909cae118 ("drm/panthor: Add the device logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Adrian Larumbe <adrian.larumbe@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241211075419.2333731-2-boris.brezillon@collabora.com