arch/arm64: fix typo in a comment

Fix typo in a comment in arch/arm64/include/asm/esr.h

"Unallocted" -> "Unallocated"

Signed-off-by: Chenggang Wang <wangchenggang@vivo.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>