Fix modules build of AVRAsmParser.cpp

Summary:
Without this change I get the following error:

lib/Target/AVR/AVRGenAsmMatcher.inc:1135:1: error: redundant #include of module 'LLVM_Utils.Support.Format' appears within namespace 'llvm' [-Wmodules-import-nested-redundant]

Reviewers: dylanmckay

Reviewed By: dylanmckay

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53425

llvm-svn: 346750