d_path: fix Kernel doc validator complaining

Kernel doc validator complains:
  Function parameter or member 'p' not described in 'prepend_name'
  Excess function parameter 'buffer' description in 'prepend_name'

Link: https://lkml.kernel.org/r/20211011005614.26189-1-justin.he@arm.com


Fixes: ad08ae58 ("d_path: introduce struct prepend_buffer")
Signed-off-by: Jia He <justin.he@arm.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>