RDMA/mlx5: Fix memory leak in GET_DATA_DIRECT_SYSFS_PATH handler

RDMA/mlx5: Fix memory leak in GET_DATA_DIRECT_SYSFS_PATH handler

The UVERBS_HANDLER(MLX5_IB_METHOD_GET_DATA_DIRECT_SYSFS_PATH) function
allocates memory for the device path using kobject_get_path(). If the
length of the device path exceeds the output buffer length, the function
returns -ENOSPC but does not free the allocated memory, resulting in a
memory leak.

Add a kfree() call to the error path to ensure the allocated memory is
properly freed.

Compile tested only. Issue found using a prototype static analysis tool
and code review.

Fixes: ec7ad6530909 ("RDMA/mlx5: Introduce GET_DATA_DIRECT_SYSFS_PATH ioctl")
Signed-off-by: Zilin Guan <zilin@seu.edu.cn>
Link: https://patch.msgid.link/20260126074801.627898-1-zilin@seu.edu.cn
Signed-off-by: Leon Romanovsky <leon@kernel.org>