sw64: simplify __phys_addr and __virt_addr_valid

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56OLG



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In these methods, the local variable `y` is redundant and can be
removed.

Signed-off-by: He Chuyue <hechuyue@wxiat.com>

Signed-off-by: Gu Zitao <guzitao@wxiat.com>