Staging: rtl8723bs: core: Remove typecast in kfree

Remove typecast in kfree, as per definition of kfree in
include/linux/slab.h#L144, the parameter type of kfree is void*, and
hence C compiler casts any pointer type to void*.

Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>