[nvptx] Fix Wformat in nvptx_assemble_decl_begin

[nvptx] Fix Wformat in nvptx_assemble_decl_begin

I'm running into this warning:
...
src/gcc/config/nvptx/nvptx.c: In function \
  ‘void nvptx_assemble_decl_begin(FILE*, const char*, const char*, \
  const_tree, long int, unsigned int, bool)’:
src/gcc/config/nvptx/nvptx.c:2229:29: warning: format ‘%d’ expects argument \
  of type ‘int’, but argument 5 has type ‘long unsigned int’ [-Wformat=]
     elt_size * BITS_PER_UNIT);
                             ^
...
which I seem to have introduced in commit b9c7fe59f9f "[nvptx] Fix array
dimension in nvptx_assemble_decl_begin", but not noticed due to configuring
with --disable-build-format-warnings.

Fix this by using the appropriate format.

Rebuild cc1 on nvptx.

gcc/ChangeLog:

	* config/nvptx/nvptx.c (nvptx_assemble_decl_begin): Fix Wformat
	warning.