scsi: st: Replace GFP_ATOMIC with GFP_KERNEL in new_tape_buffer

new_tape_buffer() is never called in atomic context. new_tape_buffer()
is only called by st_probe(), which is only set as ".probe" in struct
scsi_driver.

Despite never getting called from atomic context, new_tape_buffer()
calls kzalloc() with GFP_ATOMIC, which does not sleep for allocation.
GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL, which
can sleep and improve the possibility of sucessful allocation.

This is found by a static analysis tool named DCNS written by myself.
And I also manually check it.
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/st.c

@@ -3878,7 +3878,7 @@ static struct st_buffer *new_tape_buffer(int need_dma, int max_sg)
 {
 	struct st_buffer *tb;
 
-	tb = kzalloc(sizeof(struct st_buffer), GFP_ATOMIC);
+	tb = kzalloc(sizeof(struct st_buffer), GFP_KERNEL);
 	if (!tb) {
 		printk(KERN_NOTICE "st: Can't allocate new tape buffer.\n");
 		return NULL;
@@ -3889,7 +3889,7 @@ static struct st_buffer *new_tape_buffer(int need_dma, int max_sg)
 	tb->buffer_size = 0;
 
 	tb->reserved_pages = kzalloc(max_sg * sizeof(struct page *),
-				     GFP_ATOMIC);
+				     GFP_KERNEL);
 	if (!tb->reserved_pages) {
 		kfree(tb);
 		return NULL;