ath9k: enable serialize_regmode for non-PCIE AR9287

commit 7508b657967cf664b5aa0f6367d05016e7e3bc2a upstream.

https://bugzilla.kernel.org/show_bug.cgi?id=42903

Based on the work of <fynivx@gmail.com>

Signed-off-by: Panayiotis Karabassis <panayk@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>