mtd: update help of CONFIG_MTD_OF_PARTS

The help text of CONFIG_MTD_OF_PARTS refers to additional documentation
in booting-without-of.txt but this documentation was moved to another
file in commit efcc2da3 (Stefan Roese:
Factor MTD physmap bindings out of booting-without-of). This updates the
help text to point to the right place.
Signed-off-by: NMichal Sojka <sojkam1@fel.cvut.cz>
[Brian: fixed doc reference]
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>

drivers/mtd/Kconfig

@@ -133,7 +133,7 @@ config MTD_OF_PARTS
 	help
 	  This provides a partition parsing function which derives
 	  the partition map from the children of the flash node,
-	  as described in Documentation/devicetree/booting-without-of.txt.
+	  as described in Documentation/devicetree/bindings/mtd/partition.txt.
 
 config MTD_AR7_PARTS
 	tristate "TI AR7 partitioning support"