Add a workaround patch to fix kernel panic after ESATA disk connection

src/patches/README

 Patches from this directory are applied by 'meta-elphel393/recipes-kernel/linux/linux-xlnx' bitbake recipe. To add a new patch, append SRC_URI variable in the recipe.
+Short description of the paches:
+
+libata-eh.c.patch
+	This patch is a workaround for the situation when ESATA disk connection leads to kernel panic. Consider the following execution path in driver: libata-core.c:ata_exec_internal_sg -> error during command execution leading to command timeout -> libata-core.c:ata_qc_complete (or ata_port_freeze and finally to the same function) -> libata-core.c:ata_qc_schedule_eh where qc->scsicmd is a NULL pointer by the moment. This patch may not be needed when all hardware/software issues are rectified.

src/patches/libata-eh.c.patch

+diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
+index d2029a4..3fdf705 100644
+--- a/drivers/ata/libata-eh.c
++++ b/drivers/ata/libata-eh.c
+@@ -968,7 +968,7 @@ static void ata_eh_set_pending(struct ata_port *ap, int fastdrain)
+ void ata_qc_schedule_eh(struct ata_queued_cmd *qc)
+ {
+ 	struct ata_port *ap = qc->ap;
+-	struct request_queue *q = qc->scsicmd->device->request_queue;
++	struct request_queue *q;
+ 	unsigned long flags;
+ 
+ 	WARN_ON(!ap->ops->error_handler);
+@@ -981,9 +981,12 @@ void ata_qc_schedule_eh(struct ata_queued_cmd *qc)
+ 	 * Note that ATA_QCFLAG_FAILED is unconditionally set after
+ 	 * this function completes.
+ 	 */
+-	spin_lock_irqsave(q->queue_lock, flags);
+-	blk_abort_request(qc->scsicmd->request);
+-	spin_unlock_irqrestore(q->queue_lock, flags);
++	if (qc->scsicmd != NULL) {
++		q = qc->scsicmd->device->request_queue;
++		spin_lock_irqsave(q->queue_lock, flags);
++		blk_abort_request(qc->scsicmd->request);
++		spin_unlock_irqrestore(q->queue_lock, flags);
++	}
+ }
+ 
+ /**