arm64: pgtable-hwdef.h: delete duplicated words

Drop the repeated words "at" and "the".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20200726003207.20253-2-rdunlap@infradead.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>