wifi: airo: avoid uninitialized warning in airo_get_rate()

Quieten a gcc (11.3.0) build error or warning by checking the function
call status and returning -EBUSY if the function call failed.
This is similar to what several other wireless drivers do for the
SIOCGIWRATE ioctl call when there is a locking problem.

drivers/net/wireless/cisco/airo.c: error: 'status_rid.currentXmitRate' is used uninitialized [-Werror=uninitialized]

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/39abf2c7-24a-f167-91da-ed4c5435d1c4@linux-m68k.org
Link: https://lore.kernel.org/r/20230709133154.26206-1-rdunlap@infradead.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>