scsi: qla2xxx: Fix gnl.l memory leak on adapter init failure

If HBA initialization fails unexpectedly (exiting via probe_failed:), we
may fail to free vha->gnl.l. So that we don't attempt to double free, set
this pointer to NULL after a free and check for NULL at probe_failed: so we
know whether or not to call dma_free_coherent.

Signed-off-by: Bill Kuzeja <william.kuzeja@stratus.com>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>