GCC reports:

  ./arch/sandbox/os/common.c: In function ‘add_image’:
  ./arch/sandbox/os/common.c:271:6: warning: cast to pointer from integer of
  	different size [-Wint-to-pointer-cast]

This is because hf->base is an unsigned long long, with the upper 32 bit
all-zeroes on 32-bit systems. The compiler doesn't see that though.

Change the cast, so we no longer warn.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>