Don't duplicate parse_vdso function prototypes, include
the header instead.
Fixes: 693f5ca08c ("kselftest: Extend vDSO selftest")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>