Fixes build error:

  LD      init/built-in.o
  LD      vmlinux
  SYSMAP  System.map
  OBJCOPY arch/cris/arch-v32/boot/Image
  Kernel: arch/cris/arch-v32/boot/Image is ready
  GZIP    arch/cris/arch-v32/boot/compressed/piggy.gz
  AS      arch/cris/arch-v32/boot/compressed/head.o
crisv32-axis-linux-gnu-gcc: cannot specify -o with -c or -S and multiple compilations
make[3]: *** [arch/cris/arch-v32/boot/compressed/head.o] Error 1
make[2]: *** [arch/cris/arch-v32/boot/compressed/vmlinux] Error 2
make[1]: *** [zImage] Error 2
make: *** [sub-make] Error 2

Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>