samples: fix binderfs sample

samples: fix binderfs sample

A routine check for misspelled Kconfig symbols showed on instance
from last year, the correct symbol name is CONFIG_ANDROID_BINDERFS,
not CONFIG_CONFIG_ANDROID_BINDERFS, so the extra prefix must
be removed in the Kconfig file to allow enabling the sample.

As the actual sample fails to build as a kernel module, change the
Makefile enough to get to build as a hostprog instead.

Fixes: 9762dc1432e1 ("samples: add binderfs sample program")
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Christian Brauner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>