[SCSI] st: fix enlarge_buffer

This patch removes a bug in enlarge_buffer() that can make a
read or write fail under special conditions.

After changing TRY_DIRECT_IO to 0 and ST_MAX_SG to 32 in
st_options.h, a program that writes a first block of 128k and
than a second bigger block (e.g. 256k) fails. The second write
returns errno EOVERFLOW, as enlarge_buffer() checks the sg list
and detects that it already is full.
As enlarge_buffer uses different page allocation orders
depending on the size of the buffer needed, the check does not
make sense.

Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/st.c

@@ -3719,7 +3719,7 @@ static struct st_buffer *new_tape_buffer(int need_dma, int max_sg)
 
 static int enlarge_buffer(struct st_buffer * STbuffer, int new_size, int need_dma)
 {
-	int segs, nbr, max_segs, b_size, order, got;
+	int segs, max_segs, b_size, order, got;
 	gfp_t priority;
 
 	if (new_size <= STbuffer->buffer_size)
@@ -3729,9 +3729,6 @@ static int enlarge_buffer(struct st_buffer * STbuffer, int new_size, int need_dm
 		normalize_buffer(STbuffer);  /* Avoid extra segment */
 
 	max_segs = STbuffer->use_sg;
-	nbr = max_segs - STbuffer->frp_segs;
-	if (nbr <= 0)
-		return 0;
 
 	priority = GFP_KERNEL | __GFP_NOWARN;
 	if (need_dma)