contrib/elf2dmp: Assume error by default

contrib/elf2dmp: Assume error by default

A common construct in contrib/elf2dmp is to set "err" flag and goto
in error paths. In such a construct, there is only one successful path
while there are several error paths, so it will be more simpler to
initialize "err" flag set, and clear it in the successful path.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
Message-id: 20240307-elf2dmp-v4-2-4f324ad4d99d@daynix.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>