powerpc/time: Remove get_tbl()

There are no more users of get_tbl(). Remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/dd0368bfd497ffe06b31ee1b5f2ebf7760e30900.1612866360.git.christophe.leroy@csgroup.eu