lib/scatterlist.c: fix kerneldoc for sg_pcopy_{to,from}_buffer()

The kerneldoc for the functions doesn't match the code; the last two
parameters (buflen, skip) have been transposed, which is confusing,
especially as they're both integral types and the compiler won't warn
about swapping them.

These functions and the kerneldoc were introduced in commit:
    df642cea lib/scatterlist: introduce sg_pcopy_from_buffer() ...
    Author: Akinobu Mita <akinobu.mita@gmail.com>
    Date:   Mon Jul 8 16:01:54 2013 -0700

    The only difference between sg_pcopy_{from,to}_buffer() and
    sg_copy_{from,to}_buffer() is an additional argument that
    specifies the number of bytes to skip the SG list before
    copying.

The functions have the extra argument at the end, but the kerneldoc
lists it in penultimate position.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>