[binutils-gdb] Fix name of ser_base_setstopbits's second argument.

[sergiodj+buildbot@redhat.com]

*** TEST RESULTS FOR COMMIT 393bd0c06b64ff6076f28053cbd2fce352023c70 ***

Author: Yurij Grechishhev <yurij.grechishhev@gmail.com>
Branch: master
Commit: 393bd0c06b64ff6076f28053cbd2fce352023c70

Fix name of ser_base_setstopbits's second argument.
Small copy/paste error, most likely...

gdb/ChangeLog:

	* ser-base.h (ser_base_setstopbits): Change second argument name
	from "rate" to "num".