EFI, x86: fix function prototype

Fix function prototype in header file to match source code:

linux-next-20080807/arch/x86/kernel/efi_64.c:100:14: error: symbol 'efi_ioremap' redeclared with different type (originally declared at include2/asm/efi.h:89) - different address spaces

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>