UnnecessaryLet: fix false positive in call chains

[t-kameyama]

Fixes #5701

[codecov]

Codecov Report

Merging #6052 (07b4287) into main (1b943d6) will increase coverage by 0.01%.
The diff coverage is 91.66%.

@@             Coverage Diff              @@
##               main    #6052      +/-   ##
============================================
+ Coverage     84.85%   84.87%   +0.01%     
- Complexity     3949     3954       +5     
============================================
  Files           561      561              
  Lines         13256    13253       -3     
  Branches       2315     2314       -1     
============================================
  Hits          11248    11248              
  Misses          868      868              
+ Partials       1140     1137       -3     

Impacted Files	Coverage Δ
...ab/arturbosch/detekt/rules/style/UnnecessaryLet.kt	89.36% <91.66%> (+5.36%)	⬆️

[TWiStErRob]

Thank you @t-kameyama! 🙏