b43: Declare at least one real firmware file using MODULE_FIRMWARE.

BugLink: http://bugs.launchpad.net/bugs/488636
Enhances module information with the names of the firmware files
that could be used by this driver. This helps tools like Jockey to
correctly detect and/or install the firmware files relevant to
this driver.

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>