device property: Remove some casts in property-entry-test

With some of the stricter type checking in KUnit's EXPECT macros
removed, several casts in property-entry-test are no longer required.

Remove the unnecessary casts, making the conditions clearer.

Signed-off-by: David Gow <davidgow@google.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>