mm: Remove unused variable idx0 in __early_ioremap()

After commit:

   8827247ffcc ("x86: don't define __this_fixmap_does_not_exist()")

variable idx0 is no longer needed, so just remove it.

Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <linux-mm@kvack.org>
Cc: <wangchen@cn.fujitsu.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Link: http://lkml.kernel.org/r/5209A173.3090600@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>