lava-expect/spm-edk2-uart0.exp: Correct syntax to adhere to lava-expect spec

Due to perculiarities of LAVA interactive test handling, prompts vs commands
vs successes work a bit differently than the prompts alone. This correction
is similar to changes applied previously to other lava-expect scripts.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I22df2eab8eb3c4b68a071ed3479be0efc0e403ce
1 file changed