ARM: s3c24xx: make H1940BT depend on RFKILL

Bluetooth is only supported when network support is part of the kernel,
so it is a bit pointless to build the hi1940-bt support without networking.
If we try anyway, we get a Kconfig warning:

warning: (TOSA_BT && H1940BT) selects RFKILL which has unmet direct dependencies (NET)

This turns the 'select' into 'depends on' as Krzysztof suggested when
I first sent a fix.

Suggested-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://patchwork.kernel.org/patch/8164161/


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>