staging/olpc: fix dependencies to fix build errors

Fix build errors when GPIO_CS5535=m and FB_OLPC_DCON=y
by preventing that kconfig combination.

These build errors are caused by having a kconfig bool symbol
(FB_OLPC_DCON_1) that depend on a tristate symbol (GPIO_CS5535),
but when the tristate symbol is =m, the bool symbol is =y.

drivers/built-in.o: In function `dcon_read_status_xo_1':
olpc_dcon_xo_1.c:(.text+0x359531): undefined reference to `cs5535_gpio_set'
drivers/built-in.o: In function `dcon_wiggle_xo_1':
olpc_dcon_xo_1.c:(.text+0x35959f): undefined reference to `cs5535_gpio_set'
olpc_dcon_xo_1.c:(.text+0x359610): undefined reference to `cs5535_gpio_clear'
drivers/built-in.o:olpc_dcon_xo_1.c:(.text+0x3596a1): more undefined references to `cs5535_gpio_clear' follow
drivers/built-in.o: In function `dcon_wiggle_xo_1':
olpc_dcon_xo_1.c:(.text+0x359708): undefined reference to `cs5535_gpio_set'
drivers/built-in.o: In function `dcon_init_xo_1':
olpc_dcon_xo_1.c:(.text+0x35989b): undefined reference to `cs5535_gpio_clear'
olpc_dcon_xo_1.c:(.text+0x3598b5): undefined reference to `cs5535_gpio_isset'
olpc_dcon_xo_1.c:(.text+0x359963): undefined reference to `cs5535_gpio_setup_event'
olpc_dcon_xo_1.c:(.text+0x359980): undefined reference to `cs5535_gpio_set_irq'
olpc_dcon_xo_1.c:(.text+0x359a36): undefined reference to `cs5535_gpio_set'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc:	Daniel Drake <dsd@laptop.org>
Cc:	Jens Frederich <jfrederich@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/olpc_dcon/Kconfig

 config FB_OLPC_DCON
 	tristate "One Laptop Per Child Display CONtroller support"
 	depends on OLPC && FB
+	depends on (GPIO_CS5535 || GPIO_CS5535=n)
 	select I2C
 	select BACKLIGHT_CLASS_DEVICE
 	---help---