dm: Avoid accessing seq directly

At present various drivers etc. access the device's 'seq' member directly.
This makes it harder to change the meaning of that member. Change access
to go through a function instead.

The drivers/i2c/lpc32xx_i2c.c file is left unchanged for now.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/spi.h b/include/spi.h
index 6b42b3e..a0342e3 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -116,7 +116,7 @@
  *			claimed.
  * @bus:		ID of the bus that the slave is attached to. For
  *			driver model this is the sequence number of the SPI
- *			bus (bus->seq) so does not need to be stored
+ *			bus (dev_seq(bus)) so does not need to be stored
  * @cs:			ID of the chip select connected to the slave.
  * @mode:		SPI mode to use for this slave (see SPI mode flags)
  * @wordlen:		Size of SPI word in number of bits