powerpc/pseries: Simplify H_GET_TERM_CHAR

plpar_get_term_char is only used once and just adds a layer
of complexity to H_GET_TERM_CHAR. plpar_put_term_char isn't
used at all so we can remove it.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>