xfs_io: set argmax to 1 for imap command

xfs_io: set argmax to 1 for imap command

The imap command supports an optional argument to specify the
number of inode records to capture per ioctl(), but argmax is
currently set to 0. This leads to an error if an argument is
provided on the command line. Set argmax to 1 to support the
optional argument.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>