buildgcc: Fix typo in check for failed iasl build

Change-Id: I3e90b90e807ae775ac66af160a0f8547dcb3597a
Signed-off-by: Peter Stuge <peter@stuge.se>
Reviewed-on: http://review.coreboot.org/164
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
1 file changed