kselftest/arm64: mte: user_mem: rework error handling

kselftest/arm64: mte: user_mem: rework error handling

Future commits will have multiple iterations of tests in this function,
so make the error handling assume it will pass and then bail out if there
is an error.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220209152240.52788-3-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>