loader/i386/xnu: Fix uninitialized scalar variable

loader/i386/xnu: Fix uninitialized scalar variable

In the function grub_xnu_boot_resume(), struct grub_relocator32_state state is
called but isn't being initialized. This results in the members grub_uint32_t
ebx, grub_uint32_t ecx, grub_uint32_t edx, grub_uint32_t esi, and grub_uint32_t
edi being filled with junk data from the stack since none of them are being set
to any values. We can prevent this by setting state to {0}.

Fixes: CID 375031
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>