rtlwifi: use kcalloc instead of multiply

This is merged by Ping-Ke Shih from commit 85d309d5 ("staging:
rtlwifi: use kcalloc instead of multiply"), and original commit log
is reserved below.

checkpatch emits multiple warnings of type

WARNING:ALLOC_WITH_MULTIPLY: Prefer kcalloc over kzalloc with multiply

Replace two calls to kzalloc() with calls to kcalloc().

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>