blk-mq: fix redundant check of !e expression

In the if branch, e is checked.  In the else branch, ->dispatch_busy is
merely a number and has no effect on !e.  We should remove the check of
!e since it is always true.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Link: https://lore.kernel.org/r/20211029202945.3052-1-sakiwit@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>