powerpc/rtas: Fix whitespace in rtas_entry.S

The code was moved verbatim including whitespace cruft. Fix that.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220308135047.478297-4-npiggin@gmail.com