scsi: qedi: Initialize the stats mutex lock

Fix kernel NULL pointer dereference,

Call Trace:
  [<ffffffff9b7658e6>] __mutex_lock_slowpath+0xa6/0x1d0
  [<ffffffff9b764cef>] mutex_lock+0x1f/0x2f
  [<ffffffffc061b5e1>] qedi_get_protocol_tlv_data+0x61/0x450 [qedi]
  [<ffffffff9b1f9d8e>] ? map_vm_area+0x2e/0x40
  [<ffffffff9b1fc370>] ? __vmalloc_node_range+0x170/0x280
  [<ffffffffc0b81c3d>] ? qed_mfw_process_tlv_req+0x27d/0xbd0 [qed]
  [<ffffffffc0b6461b>] qed_mfw_fill_tlv_data+0x4b/0xb0 [qed]
  [<ffffffffc0b81c59>] qed_mfw_process_tlv_req+0x299/0xbd0 [qed]
  [<ffffffff9b02a59e>] ? __switch_to+0xce/0x580
  [<ffffffffc0b61e5b>] qed_slowpath_task+0x5b/0x80 [qed]

Signed-off-by: Nilesh Javali <nilesh.javali@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>