mwl8k: changing mwl8k_destroy_ba prototype

Currently, mwl8k_ampdu_stream is passed as one of the
argument to the function mwl8k_destroy_ba. Instead of
this pass only the stream index. This will be helpful
during watchdog event handling when bitmap of stream
indices are received.

Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>