kernel: acct.c: fix some kernel-doc nits

Fix kernel-doc notation to use the documented Returns: syntax and place
the function description for acct_process() on the first line where it
should be.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Link: https://lkml.kernel.org/r/b4c33e5d-98e8-0c47-77b6-ac1859f94d7f@infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>