spi: at25 driver is for EEPROM not FLASH

Add comment to at25 driver that it's for EEPROM chips, not FLASH
chips ... the AT25 series has both types of chip, and sometimes
they're even pin-compatible.  The command sets are different, as
is the treatment of erasure.  (FLASH needs explicit erasure, but
with EEPROM it's implicit.)  Note that all vendors seem to have
this same confusion in their *25* series SPI memory parts.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/spi/at25.c

@@ -21,6 +21,13 @@
 #include <linux/spi/eeprom.h>
 
 
+/*
+ * NOTE: this is an *EEPROM* driver.  The vagaries of product naming
+ * mean that some AT25 products are EEPROMs, and others are FLASH.
+ * Handle FLASH chips with the drivers/mtd/devices/m25p80.c driver,
+ * not this one!
+ */
+
 struct at25_data {
 	struct spi_device	*spi;
 	struct mutex		lock;