staging: rtl8192x: fix bogus maybe-uninitialized warning

The rtllib_rx_extract_addr() is supposed to set up the mac addresses
for four possible cases, based on two bits of input data. For
some reason, gcc decides that it's possible that none of the these
four cases apply and the addresses remain uninitialized:

drivers/staging/rtl8192e/rtllib_rx.c: In function ‘rtllib_rx_InfraAdhoc’:
include/linux/etherdevice.h:316:61: error: ‘*((void *)&dst+4)’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/staging/rtl8192e/rtllib_rx.c:1318:5: note: ‘*((void *)&dst+4)’ was declared here
ded from /git/arm-soc/drivers/staging/rtl8192e/rtllib_rx.c:40:0:
include/linux/etherdevice.h:316:36: error: ‘dst’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
drivers/staging/rtl8192e/rtllib_rx.c:1318:5: note: ‘dst’ was declared here

This warning is clearly nonsense, but changing the last case into
'default' makes it obvious to the compiler too, which avoids the
warning and probably leads to better object code too.

As the same warning appears in other files that have the exact
same code, I'm fixing it in both rtl8192e and rtl8192u, even
though I did not observe it for the latter.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>