staging: lustre: fix sparse warning on LPROC_SEQ_FOPS macros

This patch fix a sparse warning in lustre sources

warning: incorrect type in argument 1 (different address spaces)
    expected void [noderef] <asn:1>*to
    got char *<noident>

This is done by adding the missing __user attribute on userland pointers inside the LPROC_SEQ_FOPS like macros:
- LPROC_SEQ_FOPS
- LPROC_SEQ_FOPS_RW_TYPE
- LPROC_SEQ_FOPS_WR_ONLY
- LDLM_POOL_PROC_WRITER

The patch also updates all the functions that are used by this macro:
- lprocfs_wr_*
- *_seq_write

as well as some helpers used by the previously modified functions (otherwise fixing the sparse warning add some new ones):
- lprocfs_write_frac_helper
- lprocfs_write_helper
- lprocfs_write_u64_helper

The patch also fixes one __user pointer direct dereference by strncmp in function fld_proc_hash_seq_write.

Signed-off-by: Tristan Lelong <tristan@lelong.xyz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>