staging/lustre: Different prototypes between the declaration and the definition

Align the prototype of lprocfs_wr_uint() in the declaration with the one used
in the definition.

The prototype is:
int lprocfs_wr_uint(struct file *file, const char __user *buffer,
                    unsigned long count, void *data)
In obdclass/lprocfs_status.c

But in lustre/include/lprocfs_status.h, the __user annotation is missing for
the attribute buffer.

The correct prototype is the first one (the definition) since:
- This function is eventually called by the write() function pointer of an
instance of struct file_operations
- In this function, buffer is a parameter of copy_from_user()
- Before the commit 73bb1da6, the declaration
and the definition had the same prototype, but only the .c has been updated.

Correcting this will remove a sparse error and add sparse warnings.
This is a task of the Eudyptula challenge.

Signed-off-by: Loïc Pellegrino <oort10@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>