analyzer: fix duplicates in check_for_tainted_size_arg

analyzer: fix duplicates in check_for_tainted_size_arg

gcc/analyzer/ChangeLog:
	* sm-taint.cc (taint_state_machine::check_for_tainted_size_arg):
	Avoid generating duplicate saved_diagnostics by only handling the
	rdwr_map entry for the ptrarg, not the duplicate entry for the
	sizarg.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/taint-size-access-attr-1.c: Add
	-fanalyzer-show-duplicate-count to options; verify that a
	duplicate was not created for the tainted size.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>