mwifiex: move usb specific data_sent update to usb.c

This patch move data_sent flag update to usb.c file.
>From now all data_sent update cases only happened in specific file:
sdio.c, usb.c, pcie.c. Outside ot these files, it is only allowed
to check the value of data_ent.

Signed-off-by: Zhaoyang Liu <liuzy@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>