dfc/platform: Fix wrong cast.

`typecmp` works on an array of string (const char*) and its arguments
are pointers to a const element of the array.
Thus the argument's type is a pointer to a const pointer to const char
(const char * const *), not a pointer to a       pointer to const char
(const char **).

Signed-off-by: Sylvain Laperche <sylvain.laperche@gmail.com>