scripts/kernel-doc: handle struct member __aligned

scripts/kernel-doc erroneously says:

Warning(include/linux/skbuff.h:410): Excess struct/union/enum/typedef member 'cb' description in 'sk_buff'

on this line in struct sk_buff:
	char			cb[48] __aligned(8);

due to treating the last field as the struct member name, so teach
kernel-doc to ignore __aligned(x) in structs.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>