mei: replace POLL* with EPOLL* for write queues.

Looks like during merging the bulk POLL* -> EPOLL* replacement
missed the patch
'commit af336cab ("mei: limit the number of queued writes")'

Fix sparse warning:
drivers/misc/mei/main.c:602:13: warning: restricted __poll_t degrades to integer
drivers/misc/mei/main.c:605:30: warning: invalid assignment: |=
drivers/misc/mei/main.c:605:30:    left side has type restricted __poll_t
drivers/misc/mei/main.c:605:30:    right side has type int

Fixes: af336cab ("mei: limit the number of queued writes")
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>