bdk: sdmmc: homogenize return values

The actual target of this refactoring.

bdk/storage/sd.h

@@ -55,8 +55,8 @@ bool sd_get_card_initialized();
 bool sd_get_card_mounted();
 u32  sd_get_mode();
 int  sd_init_retry(bool power_cycle);
-bool sd_initialize(bool power_cycle);
-bool sd_mount();
+int  sd_initialize(bool power_cycle);
+int  sd_mount();
 void sd_unmount();
 void sd_end();
 bool sd_is_gpt();