powerpc/selftest: fix type of mftb() in null_syscall

[Michael Ellerman]

On Tue, 2019-01-22 at 13:54:57 UTC, Christophe Leroy wrote:
> All callers of mftb() expect 'unsigned long', and the function itself
> only returns lower part of the TB so it really is 'unsigned long'
> not 'unsigned long long'
> 
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/beb4f4722cf60d9f0803054dec4eb502

cheers