staging: rtl8723bs: Use min() instead of doing it manually

Fix following coccicheck warning:
drivers/staging/rtl8723bs/core/rtw_xmit.c:452:25-26: WARNING opportunity for min()

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Link: https://lore.kernel.org/r/1646983052-16390-1-git-send-email-baihaowen@meizu.com


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