FIX: Connect derivatives mask to mcribs recon

[mgxd]

Running --surface-recon mcribs with a derivative mask would cause the process to hang indefinitely.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (9293858) 32.81% compared to head (c1d9e11) 32.80%.

Files	Patch %	Lines
nibabies/workflows/anatomical/base.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #323      +/-   ##
==========================================
- Coverage   32.81%   32.80%   -0.02%     
==========================================
  Files          55       55              
  Lines        5315     5317       +2     
==========================================
  Hits         1744     1744              
- Misses       3571     3573       +2     

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