BugLink: https://bugs.launchpad.net/bugs/1855313

[ Upstream commit 2b6f0090 ]

add_mtd_device() can fail. We should always check its return value
and gracefully handle the failure case. Fix the call sites where this
not done (in mtdpart.c) and add a __must_check attribute to the
prototype to avoid this kind of mistakes.
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>