Replace BSD-3-clause-Smrgrav with BSD-3-clause-Miller

I noticed that this last word is the surname of the copyright holder who
decided to use a different version of the license, so it should be
Miller, not Smrgrav. Smrgrav is the surname of a copyright holder in another
package that I found with Codesearch.
8 jobs for debian/2.0.4-1 in 13 minutes and 16 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #257501
build

00:03:19

 
  Test
passed #257506
autopkgtest

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passed #257507
blhc

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passed #257505
lintian

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passed #257508
piuparts

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passed #257504
reprotest

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passed #257503
test-build-all

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passed #257502
test-build-any

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