mtd: spi-nor: silently drop lock/unlock for already locked/unlocked region

If, for instance, the entire flash is already unlocked and I try to
mtd_unlock() the entire device, I don't expect to see an EINVAL error.
It should just silently succeed. Ditto for mtd_lock().
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

drivers/mtd/spi-nor/spi-nor.c

@@ -515,8 +515,12 @@ static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_new = (status_old & ~mask) | val;
 
+	/* Don't bother if they're the same */
+	if (status_new == status_old)
+		return 0;
+
 	/* Only modify protection if it will not unlock other areas */
-	if ((status_new & mask) <= (status_old & mask))
+	if ((status_new & mask) < (status_old & mask))
 		return -EINVAL;
 
 	write_enable(nor);
@@ -569,8 +573,12 @@ static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_new = (status_old & ~mask) | val;
 
+	/* Don't bother if they're the same */
+	if (status_new == status_old)
+		return 0;
+
 	/* Only modify protection if it will not lock other areas */
-	if ((status_new & mask) >= (status_old & mask))
+	if ((status_new & mask) > (status_old & mask))
 		return -EINVAL;
 
 	write_enable(nor);