allow emmc writes (to write warmboot to emusd), allow unaligned emmc writes

fusee/program/source/fatfs/fusee_diskio.cpp

@@ -32,8 +32,7 @@ bool diskio_read_system(void *dst, size_t size, size_t sector_index, size_t sect
 }
 
 bool diskio_write_system(size_t sector_index, size_t sector_count, const void *src, size_t size) {
-    /* Don't allow writes to eMMC GPP partition */
-    return false;
+    return R_SUCCEEDED(::ams::nxboot::WriteMmc(::ams::sdmmc::MmcPartition::MmcPartition_UserData, sector_index, sector_count, src, size));
 }
 
 bool diskio_read_boot1(void *dst, size_t size, size_t sector_index, size_t sector_count) {