ice: Fix potential memory leak in ice_gnss_tty_write()

The ice_gnss_tty_write() return directly if the write_buf alloc failed,
leaking the cmd_buf.

Fix by free cmd_buf if write_buf alloc failed.

Fixes: d6b98c8d ("ice: add write functionality for GNSS TTY")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>