workqueue: fix texinfodocs warning for WQ_* flags reference

Sphinx emitted a warning during make texinfodocs:

WARNING: Inline literal start-string without end-string.

This was caused by the trailing '*' in "%WQ_*" being parsed as
reStructuredText markup in the kernel-doc comment.

Escape the '*' in the comment so that Sphinx treats it as a literal
character, resolving the warning.

Signed-off-by: Kriish Sharma <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

include/linux/workqueue.h

···
  * min_active which is set to min(@max_active, %WQ_DFL_MIN_ACTIVE). This means
  * that the sum of per-node max_active's may be larger than @max_active.
  *
- * For detailed information on %WQ_* flags, please refer to
+ * For detailed information on %WQ_\* flags, please refer to
  * Documentation/core-api/workqueue.rst.
  *
  * RETURNS: