[IA64] fix number of bytes zeroed by sys_fw_init() in arch/ia64/hp/sim/boot/fw-emu.c

The sizeof a pointer is constant, we want the sizeof what is pointed to.
Zero out 'sizeof(*efi_systab)' bytes of the efi_system_table_t pointer
'efi_systab' instead.

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Signed-off-by: Tony Luck <tony.luck@intel.com>