kbuild: fix space for good (take 103)

Michal Ostrowski points out what the real problem was: the spaces at the
start of the definition of the 'checker-shell' make function.

Cc: Michal Ostrowski <mostrows@watson.ibm.com>
Acked-by: David Miller <davem@davemloft.net>
Acked-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Oleg Verych <olecom@flower.upol.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>