BPF: fix a buildbot test failure

Commit 737e4216 ("[Attr] support btf_type_tag attribute")
added btf_type_tag support in llvm. Buildbot reported a
failure with attr-btf_type_tag.ll.

  ; CHECK-NEXT: DW_AT_type (0x[[T1:[0-9]+]] "int ***")

  <stdin>:15:2: note: possible intended match here
   DW_AT_type (0x0000002f "int ***")

The pattern [0-9]+ is not enough to match 0000002f, we
need [0-9a-f]+. This patch fixed the issue.