scsi: st: Use get_unaligned_be24() and sign_extend32()

Use these functions instead of open-coding them.

Link: https://lore.kernel.org/r/20200313203102.16613-5-bvanassche@acm.org
Cc: Kai Makisara <Kai.Makisara@kolumbus.fi>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/st.c

@@ -45,6 +45,7 @@ static const char *verstr = "20160209";
 
 #include <linux/uaccess.h>
 #include <asm/dma.h>
+#include <asm/unaligned.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_dbg.h>
@@ -2680,8 +2681,7 @@ static void deb_space_print(struct scsi_tape *STp, int direction, char *units, u
 	if (!debugging)
 		return;
 
-	sc = cmd[2] & 0x80 ? 0xff000000 : 0;
-	sc |= (cmd[2] << 16) | (cmd[3] << 8) | cmd[4];
+	sc = sign_extend32(get_unaligned_be24(&cmd[2]), 23);
 	if (direction)
 		sc = -sc;
 	st_printk(ST_DEB_MSG, STp, "Spacing tape %s over %d %s.\n",