[PATCH] powerpc: fix two build warnings

Building the arch/powerpc tree currently gives me
two warnings with gcc-4.0:

arch/powerpc/mm/imalloc.c: In function '__im_get_area':
arch/powerpc/mm/imalloc.c:225: warning: 'tmp' may be used uninitialized in this function
arch/powerpc/mm/hugetlbpage.c: In function 'hugetlb_get_unmapped_area':
arch/powerpc/mm/hugetlbpage.c:608: warning: unused variable 'vma'

both fixes are trivial.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>