arm64: mte: Clean up user tag accessors

Invoking user_ldst to explicitly add a post-increment of 0 is silly.
Just use a normal USER() annotation and save the redundant instruction.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Tong Tiangen <tongtiangen@huawei.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20220420030418.3189040-6-tongtiangen@huawei.com


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