target-sh4: Use glib allocator in movcal helper

Coverity spots that helper_movcal() calls malloc() but doesn't
check for failure. Fix this by switching to the glib allocation
functions, which abort on allocation failure.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1468327859-21385-1-git-send-email-peter.maydell@linaro.org
Acked-by: Aurelien Jarno <aurelien@aurel32.net>
