[PATCH] powerpc: Remove duplicate definition of set_tb()

Somewhere along the line we got two definitions of set_tb(). They look to
be identical although they're not textually identical. So remove the #ifdef
CONFIG_PPC64 version, leaving the common version in time.h.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>