staging: skein: fix sparse warnings related to shift operator

Fix warnings:
drivers/staging/skein/skein_base.h:89:30: warning: shift too big (50) for type int
...
drivers/staging/skein/skein_base.h:89:30: warning: shift too big (39)for type int
drivers/staging/skein/skein_base.h:89:19: warning: too many warnings

Signed-off-by: Domagoj Trsan <domagoj.trsan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>