trivial: kernel/power/poweroff.c: whitespace fix

Fix coding style whitespace fixes. Patch compile tested
Before :-
total: 1 errors, 0 warnings, 46 lines checked
After
total: 0 errors, 0 warnings, 46 lines checked

Before :-
  text	   data	    bss	    dec	    hex	filename
    107	     48	      0	    155	     9b	kernel/power/poweroff.o
After
   text	   data	    bss	    dec	    hex	filename
    107	     48	      0	    155	     9b	kernel/power/poweroff.o

Signed-off-by: Manish Katiyar <mkatiyar@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>