block: IBM RamSan 70/80 driver fixes

This patch includes the following driver fixes for the
IBM RamSan 70/80 driver:

o Changed the creg_ctrl lock from a mutex to a spinlock.
o Added a count check for ioctl calls.
o Removed unnecessary casting of void pointers.
o Made every function static that needed to be.
o Added comments to explain things more thoroughly.

Signed-off-by: Philip J Kelleher <pjk1939@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/rsxx/dev.c b/drivers/block/rsxx/dev.c
index 96df053..4346d17 100644
--- a/drivers/block/rsxx/dev.c
+++ b/drivers/block/rsxx/dev.c
@@ -149,7 +149,7 @@
 			    void *cb_data,
 			    unsigned int error)
 {
-	struct rsxx_bio_meta *meta = (struct rsxx_bio_meta *)cb_data;
+	struct rsxx_bio_meta *meta = cb_data;
 
 	if (error)
 		atomic_set(&meta->error, 1);