Fix SPDX-License-Identifier typos

Fix SPDX-License-Identifier typos

Several SPDX headers contain "SPDX-License-Identifer" (note the
missing "i" before "er"); fix these typos.

Signed-off-by: Ryan Finnie <ryan@finnie.org>
Cc: qemu-trivial@nongnu.org
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210201200147.211914-1-ryan@finnie.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>