fs/handle.c - fix up kerneldoc

When building with W=1, we get some kerneldoc warnings:

  CC      fs/fhandle.o
fs/fhandle.c:259: warning: Function parameter or member 'flags' not described in 'sys_open_by_handle_at'
fs/fhandle.c:259: warning: Excess function parameter 'flag' description in 'sys_open_by_handle_at'

Fix the typo that caused it.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>