powerpc32: fix stack allocation code generation
powerpc32: fix stack allocation code generation

When ghc was built for powerpc32 built failed as:

It's a fallout of commit 3f46cffcc2850e68405a1
("PPC NCG: Refactor stack allocation code") where
word size used to be
    II32/II64
and changed to
    II8/panic "no width for given number of bytes"
    widthFromBytes ((platformWordSize platform) `quot` 8)

The change restores initial behaviour by removing extra division.

Signed-off-by: Sergei Trofimovich <110fdadc76b6bce16977f568bdb4723eaed6fb3f@gentoo.org>

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc