arm64: cpufeatures: Clean up temporary variable to simplify code

Clean up one temporary variable to simplifiy code in capability
detection.

Signed-off-by: Liao Chang <liaochang1@huawei.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240229105208.456704-1-liaochang1@huawei.com


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