compiler: Add missing symbolic casts

[mloubout]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 87.07%. Comparing base (db692d2) to head (ef578dd).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
devito/tools/dtypes_lowering.py	0.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2462      +/-   ##
==========================================
- Coverage   87.07%   87.07%   -0.01%     
==========================================
  Files         239      239              
  Lines       45117    45123       +6     
  Branches     8427     8428       +1     
==========================================
+ Hits        39285    39289       +4     
- Misses       5100     5101       +1     
- Partials      732      733       +1     

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[FabioLuporini]

Uncontroversial