arch/m68k/include/asm/motorola_pgalloc.h: fix kunmap arg

arch/m68k/include/asm/motorola_pgalloc.h: In function 'pte_alloc_one':
arch/m68k/include/asm/motorola_pgalloc.h:44: warning: passing argument 1 of 'kunmap' from incompatible pointer type

Also, remove unneeded test for kmap() failure.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>