staging: rtl8192e: remove bogus ssid character sign test

This error triggers on some architectures with unsigned `char` types:

drivers/staging/rtl8192e/rtllib_softmac_wx.c:459 rtllib_wx_set_essid() warn: impossible condition '(extra[i] < 0) => (0-255 < 0)'

But actually, the entire test is bogus, as ssids don't have any sign
validity rules like that. So just remove this check look all together.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20221025122150.583617-1-Jason@zx2c4.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>