x86, um: Fix typo in 32-bit system call modifications

We override sys_iopl(), not stub_iopl(); the latter is a 64-bitism
that doesn't apply to i386 in the first place.
Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/um/sys_call_table_32.c

@@ -16,7 +16,7 @@
  */
 
 /* Not going to be implemented by UML, since we have no hardware. */
-#define stub_iopl sys_ni_syscall
+#define sys_iopl sys_ni_syscall
 #define sys_ioperm sys_ni_syscall
 
 #define sys_vm86old sys_ni_syscall