Fix access of cmap argument

[mcfarljm]

Closes #173. cmap was not available in kwargs because it was explicitly declared as a keyword argument.

Also considered removing the explicit cmap keyword argument, in which cmap could be contained in the kwargs dict that gets propagated to networkx.draw, but I don't think that is the intent.

[codecov-commenter]

Codecov Report

Merging #207 (1089869) into main (9213c81) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             main     #207   +/-   ##
=======================================
  Coverage   71.15%   71.15%           
=======================================
  Files          29       29           
  Lines        1751     1751           
=======================================
  Hits         1246     1246           
  Misses        505      505           

Impacted Files	Coverage Δ
dwave_networkx/drawing/qubit_layout.py	5.04% <0.00%> (ø)

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