add missing call to add new NAND devices

I forgot to add a call to the newly factored nand_device_add(), along
with its forward declaration.

src/flash/nand/imp.h

@@ -22,6 +22,8 @@
 #include "core.h"
 #include "driver.h"
 
+void nand_device_add(struct nand_device *c);
+
 int nand_write_page(struct nand_device *nand,
 		uint32_t page, uint8_t *data, uint32_t data_size,
 		uint8_t *oob, uint32_t oob_size);

src/flash/nand/tcl.c

@@ -580,6 +580,8 @@ static COMMAND_HELPER(create_nand_device, const char *bank_name,
 		return ERROR_OK;
 	}
 
+	nand_device_add(c);
+
 	return ERROR_OK;
 }