kernel: make apk_sign_key as a typedef instead

Style preference.

Signed-off-by: rsuntk <rsuntk@yukiprjkt.my.id>

kernel/manager_sign.h

@@ -11,4 +11,9 @@
 #define EXPECTED_HASH_OTHER \
 	"0000000000000000000000000000000000000000000000000000000000000000"
 
+typedef struct {
+	unsigned size;
+	const char *sha256;
+} apk_sign_key_t;
+
 #endif /* MANAGER_SIGN_H */