fix: gpu_device not defined in Flux.DistributedUtils

[AntonOresten]

gpu_device was not explicitly imported in the DistributedUtils module, leading to an UndefVarError. Instead of importing it, this PR simply calls get_device on the buffer to get the device, as is done in the bcast! method from the same file, and the original Lux.jl implementation.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 65.71%. Comparing base (9050ef0) to head (885d95d).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/distributed/public_api.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2552       +/-   ##
===========================================
+ Coverage   32.78%   65.71%   +32.93%     
===========================================
  Files          34       35        +1     
  Lines        1998     2039       +41     
===========================================
+ Hits          655     1340      +685     
+ Misses       1343      699      -644     

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