self-review: misc

- update static sampler offset now that it is computed correctly
- update test comment

Author: inbelic

llvm/test/tools/llvm-objcopy/DXContainer/extract-section-basic.test

@@ -277,7 +277,7 @@ Parts:
       NumRootParameters: 0
       RootParametersOffset: 24
       NumStaticSamplers: 0
-      StaticSamplersOffset: 0
+      StaticSamplersOffset: 24
       Parameters:      []
   - Name:            PSV0
     Size:            76

llvm/test/tools/llvm-objcopy/DXContainer/extract-section-errs.test

@@ -1,7 +1,7 @@
 ## Check that llvm-objcopy reports a suitable error when it
 ## can't find the section to extract
 
-## We can't have multiple DXIL parts.
+## We can't extract a part that doesn't exist
 # RUN: yaml2obj %s --docnum=1 -o %t1
 # RUN: not llvm-objcopy %t1 --extract-section=UNKNOWN=%t.unknown.out 2>&1 | FileCheck %s -DFILE=%t1 --check-prefix=ERROR1