drm/panfrost: Fix wait_bo ioctl leaking positive return from dma_resv_wait_timeout()

drm/panfrost: Fix wait_bo ioctl leaking positive return from dma_resv_wait_timeout()

dma_resv_wait_timeout() returns a positive 'remaining jiffies' value
on success, 0 on timeout, and -errno on failure.

panfrost_ioctl_wait_bo() returns this 'long' result from an int-typed
ioctl handler, so positive values reach userspace as bogus errors.
Explicitly set ret to 0 on the success path.

Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
Cc: stable@vger.kernel.org
Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
Reviewed-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/fe33f82fded7be1c18e2e0eb2db451d5a738cf39.1776581974.git.gye976@gmail.com
Signed-off-by: Steven Price <steven.price@arm.com>