mtd: fsmc_nand: modify the wait to uninterruptible

Interruptible wait caused trouble in fsmc hardware state machine if the
application was killed abruptly. To make fsmc operation safe turn wait in to
un-interruptible.

Signed-off-by: Vipin Kumar <vipin.kumar@st.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>