tty/serial/8250: fix typo in help text

Commit 9326b047 includes a typo
of "8350_core" instead of "8250_core", so correct it.

Fixes kernel bugzilla #60724:
  https://bugzilla.kernel.org/show_bug.cgi?id=60724



Reported-by: Christoph Biedl <bugzilla.kernel.bpeb@manchmal.in-ulm.de>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>