[ARM] 3471/1: FTOSI functions should return 0 for NaN

Patch from Catalin Marinas

The NaN case was dealed with by the "exponent >= ... + 32" condition but it
was not setting the value "d" to 0.

Signed-off-by: Ken'ichi Kuromusha <musha@aplix.co.jp>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>