mmc: sdhci-of-aspeed: Remove some unnecessary casts from KUnit tests

With KUnit's EXPECT macros no longer typechecking arguments as strictly,
get rid of a number of now unnecessary casts.

Signed-off-by: David Gow <davidgow@google.com>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>