staging: lustre: Use kstrtouint_from_user in ldlm_rw_uint

Clean up the helper functions used to implement "dump_granted_max" in
debugfs.

Replace the lprocfs_rd_uint() and lprocfs_wr_uint() generic callbacks
with a simpler, more direct implementation of ldlm_rw_uint_fops.

There's a slight change in lustre debugfs write semantics: Using kstrtox
causes EINVAL when the written number is followed by other (garbage)
characters, whereas previously the garbage would be ignored and such a
write would succeed.

Signed-off-by: Mathias Rav <mathiasrav@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>