rsi: Remove unnecessary boolean condition

Clang warns that the address of a pointer will always evaluated as true
in a boolean context.

drivers/net/wireless/rsi/rsi_91x_mac80211.c:927:50: warning: address of
array 'key->key' will always evaluate to 'true'
[-Wpointer-bool-conversion]
        if (vif->type == NL80211_IFTYPE_STATION && key->key &&
                                                ~~ ~~~~~^~~
1 warning generated.

Link: https://github.com/ClangBuiltLinux/linux/issues/136


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>