staging: rtl8712: Improve suspend/resume functionality.

Fix a driver hang caused by earlier suspend/resume cycles. By handling a
ENODEV error during suspend as a real error we eventually end up stopping
the whole driver.

Fix this by handling the ENODEV error (during suspend) essentially by
retrying.

Signed-off-by: Hemmo Nieminen <hemmo.nieminen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>