arm64: mm: fix comment typo of pud_offset_phys()

Fix a typo in the comment of macro pud_offset_phys().

Signed-off-by: Xujun Leng <lengxujun2007@126.com>
Link: https://lore.kernel.org/r/20210825150526.12582-1-lengxujun2007@126.com


Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>