efi_loader: correct parameter size in efi_allocate_pool

efi_allocate_pages() expects a (uint64_t *) pointer to pass the address of
the assigned memory. If we pass the address of a pointer here, an illegal
memory access occurs on 32bit systems.

Fixes: 282a06cb ("efi_loader: Expose U-Boot addresses in memory map
for sandbox")
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>