net/mlx5: fix return value in Rx interrupts code
net/mlx5: fix return value in Rx interrupts code

A negative return value is documented for that function in case of error.

Fixes: 3c7d44af252a ("net/mlx5: support user space Rx interrupt event")
Cc: stable@dpdk.org

Signed-off-by: Adrien Mazarguil <9d39ea493ca46c560334f650ac5d4b5ffbcb5cf0@6wind.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk