x86: fix arch/x86/kernel/cpu/mtrr/main.c warning

fix this warning reported by Andrew Morton:

> arch/x86/kernel/cpu/mtrr/main.c: In function 'mtrr_bp_init':
> arch/x86/kernel/cpu/mtrr/main.c:1170: warning: 'extra_remove_base' may be used uninitialized in this function

the warning is bogus but the logic that prevents uninitialized use
is a bit convoluted so simplify it all.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/mtrr/main.c

@@ -1218,11 +1218,10 @@ static int __init mtrr_cleanup(unsigned address_bits)
 
 	memset(range, 0, sizeof(range));
 	extra_remove_size = 0;
-	if (mtrr_tom2) {
 	extra_remove_base = 1 << (32 - PAGE_SHIFT);
+	if (mtrr_tom2)
 		extra_remove_size =
 			(mtrr_tom2 >> PAGE_SHIFT) - extra_remove_base;
-	}
 	nr_range = x86_get_mtrr_mem_range(range, 0, extra_remove_base,
 					  extra_remove_size);
 	range_sums = sum_ranges(range, nr_range);