powerpc/32s: Fix an FTR_SECTION_ELSE

An FTR_SECTION_ELSE is in the middle of
BEGIN_MMU_FTR_SECTION/ALT_MMU_FTR_SECTION_END_IFSET

Change it to MMU_FTR_SECTION_ELSE

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/61790f1a91692950a6bb5bb53d6d514d9bcdad74.1606285014.git.christophe.leroy@csgroup.eu