sh/mm: Fix pmd_t for real

Because typing is hard...

Fixes: 0862ff05

 ("sh/mm: Make pmd_t similar to pte_t")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>