scripts/dtc: Remove redundant YYLOC global declaration

gcc 10 will default to -fno-common, which causes this error at link
time:

  (.text+0x0): multiple definition of `yylloc'; dtc-lexer.lex.o (symbol from plugin):(.text+0x0): first defined here

This is because both dtc-lexer as well as dtc-parser define the same
global symbol yyloc. Before with -fcommon those were merged into one
defintion. The proper solution would be to to mark this as "extern",
however that leads to:

  dtc-lexer.l:26:16: error: redundant redeclaration of 'yylloc' [-Werror=redundant-decls]
   26 | extern YYLTYPE yylloc;
      |                ^~~~~~
In file included from dtc-lexer.l:24:
dtc-parser.tab.h:127:16: note: previous declaration of 'yylloc' was here
  127 | extern YYLTYPE yylloc;
      |                ^~~~~~
cc1: all warnings being treated as errors

which means the declaration is completely redundant and can just be
dropped.

Signed-off-by: Dirk Mueller <dmueller@suse.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[robh: cherry-pick from upstream]
Cc: stable@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>