staging: rtl8712: Remove spaces after a cast

Remove extra spaces after a cast to conform with Linux kernel coding
style.
Reported by checkpatch.

Signed-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@gmail.com>
Link: https://lore.kernel.org/r/f8932bfa35eb7480b69a9c8296bb10fac5a28540.1617697237.git.zhansayabagdaulet@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>