PCI: Check if entry->offset already exist for mem resource

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP



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Fix patch "LoongArch: Add PCI controller support"

Signed-off-by: Tianli Xiong <xiongtianli@loongson.cn>
Change-Id: I796b1224d8990fed952643adac491228d6541696