fix abs of diff of uint

[chenyuxyz]

brought up in #4188
abs to unsigned or bool is no-op
use where for int because cstyle does not like relu for int (might have more issue with int in general)
keep double relu for float, would need to check perf before switching

RHIP crashed in CI @Qazalin fyi

[github-actions]

Changes

Name                  Lines    Diff    Tokens/Line    Diff
------------------  -------  ------  -------------  ------
tinygrad/tensor.py      799      +3           21.7    -0.0


total lines changes: +3

[chenyuxyz]

fixed by the new abs #4611