accel/rocket: Fix prep_bo ioctl leaking positive return from dma_resv_wait_timeout()

accel/rocket: Fix prep_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.

rocket_ioctl_prep_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: 525ad89dd904 ("accel/rocket: Add IOCTLs for synchronizing memory accesses")
Cc: stable@vger.kernel.org
Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
Reviewed-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>
Link: https://patch.msgid.link/c0ebf83b345721701b22d8f5bc41c52c0ecf5e16.1776581974.git.gye976@gmail.com
Signed-off-by: Steven Price <steven.price@arm.com>