arm64: memory: Add missing brackets to untagged_addr() macro

Add brackets around the evaluation of the 'addr' parameter to the
untagged_addr() macro so that the cast to 'u64' applies to the result
of the expression.

Cc: <stable@vger.kernel.org>
Fixes: 597399d0

 ("arm64: tags: Preserve tags for addresses translated via TTBR1")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Will Deacon <will@kernel.org>