memory_dump: resolve the issue of configuring core_reg_numer

When the new core_reg_number value is the same as previous value,
writing to core_reg_number node cannot exit normally, this
change resolve this issue.

Change-Id: I6cbb301fc77a630aa9f01a68341c9510fdbd5c0f
Signed-off-by: Yuanfang Zhang <zhangyuanfang@codeaurora.org>