ihex: fix unused return value compiler warning

Fix unusued return value compiler warnings due to unchecked write() calls.

[akpm@linux-foundation.org: correctly handle short writes]
Signed-off-by: Chris Ruffin <cmruffin@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>