asm-generic/error-injection.h: fix a spelling mistake, and a coding style issue

Fix a spelling mistake "ganerating" -> "generating".
Remove trailing semicolon for a macro ALLOW_ERROR_INJECTION to fix a
coding style issue.

Signed-off-by: Wasin Thonkaew <wasin@wasin.io>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>