powerpc/64s: Fix unnecessary machine check handler relocation branch

Similarly to commit 2563a70c ("powerpc/64s: Remove unnecessary relocation
branch from idle handler"), the machine check handler has a BRANCH_TO from
relocated to relocated code, which is unnecessary.

It has also caused build errors with some toolchains:

  arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
  arch/powerpc/kernel/exceptions-64s.S:395: Error: operand out of range
  (0xffffffffffff8280 is not between 0x0000000000000000 and
  0x000000000000ffff)

Fixes: 1945bc45 ("powerpc/64s: Fix POWER9 machine check handler from stop state")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reported-and-tested-by : Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>