um/sysrq: remove needless variable sp

`sp' is a needless excercise here.

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Link: http://lkml.kernel.org/r/20200418201944.482088-36-dima@arista.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>