proc: spread likely/unlikely a bit

use_pde() is used at every open/read/write/...  of every random /proc
file.  Negative refcount happens only if PDE is being deleted by module
(read: never).  So it gets "likely".

unuse_pde() gets "unlikely" for the same reason.

close_pdeo() gets unlikely as the completion is filled only if there is a
race between PDE removal and close() (read: never ever).

It even saves code on x86_64 defconfig:

	add/remove: 0/0 grow/shrink: 1/2 up/down: 2/-20 (-18)
	Function                                     old     new   delta
	close_pdeo                                   183     185      +2
	proc_reg_get_unmapped_area                   119     111      -8
	proc_reg_poll                                 85      73     -12

Link: http://lkml.kernel.org/r/20180104175657.GA5204@avx2


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>