kernel-doc: Fix parsing of DECLARE_BITMAP in struct

Some documented structures in the kernel use DECLARE_BITMAP to create
arrays of unsigned longs to store information using the bitmap functions.
These have to be replaced with a parsable version for kernel-doc.

For example a simple input like

    /**
     * struct something - some test
     * @members: active members
     */
    struct something {
    	DECLARE_BITMAP(members, MAX_MEMBERS);
    };

resulted in parsing warnings like

    warning: No description found for parameter 'MAX_MEMBERS)'
    warning: Excess struct/union/enum/typedef member 'members' description in 'something'

Signed-off-by: Conchúr Navid <conchur@web.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>