spi-gpio: sanitize MISO bitvalue

gpio_get_value() returns 0 or nonzero, but getmiso() expects 0 or 1.
Sanitize the value to a 0/1 boolean.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>