wifi: p54: add missing parentheses in p54_flush()

The assignment of the value to the variable total in the loop
condition must be enclosed in additional parentheses, since otherwise,
in accordance with the precedence of the operators, the conjunction
will be performed first, and only then the assignment.

Due to this error, a warning later in the function after the loop may
not occur in the situation when it should.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Rustam Subkhankulov <subkhankulov@ispras.ru>
Fixes: 0d4171e2

 ("p54: implement flush callback")
Acked-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220714134831.106004-1-subkhankulov@ispras.ru