int is not sufficient to hold and test the return from an EFI function
call. Use efi_status_t instead so that the test can work as expected.
This issue was found by Smatch.
Fixes: 275854baee ("efi: Add a serial driver")
Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>