mtd/m25p80: retlen is never NULL

This is just a cleanup, it doesn't fix any bugs.

These functions all check retlen inconsistently and it generates a
warning in Smatch (http://smatch.sf.net). If retlen were ever NULL it
would cause an oops and the code has been this way since 2006 so someone
would have complained. Also I looked at other places that implemented
the mtd read and write functions and they dereference retlen without
checking.

I removed the checks.

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/devices/m25p80.c

···
 	spi_message_add_tail(&t[1], &m);
 
 	/* Byte count starts at zero. */
-	if (retlen)
-		*retlen = 0;
+	*retlen = 0;
 
 	mutex_lock(&flash->lock);
 
···
 			dev_name(&flash->spi->dev), __func__, "to",
 			(u32)to, len);
 
-	if (retlen)
-		*retlen = 0;
+	*retlen = 0;
 
 	/* sanity checks */
 	if (!len)
···
 
 			spi_sync(flash->spi, &m);
 
-			if (retlen)
-				*retlen += m.actual_length - m25p_cmdsz(flash);
+			*retlen += m.actual_length - m25p_cmdsz(flash);
 		}
 	}
 
···
 	size_t actual;
 	int cmd_sz, ret;
 
-	if (retlen)
-		*retlen = 0;
+	*retlen = 0;
 
 	/* sanity checks */
 	if (!len)