there is an unexpected word 'a' in the comments that need to be dropped

Link: https://lkml.kernel.org/r/24fbdae3.c86.1819a0f31b9.Coremail.chenxuebing@jari.cnSigned-off-by: NXueBing Chen <chenxuebing@jari.cn>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>