i2c-stu300: Make driver depend on MACH_U300

This makes the stu300 driver for the ST Micro ST DDC I2C bus
driver depend on MACH_U300, new platforms reusing this I2C
driver will need to add in a similar dependency.
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
[ben-linux@fluff.org: re-aranged subject line]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

drivers/i2c/busses/Kconfig

@@ -515,6 +515,7 @@ config I2C_SIMTEC
 
 config I2C_STU300
 	tristate "ST Microelectronics DDC I2C interface"
+	depends on MACH_U300
 	default y if MACH_U300
 	help
 	  If you say yes to this option, support will be included for the