fastboot: reinit partition after storing GPT or MBR

In case MMC has MBR system and fastboot writes GPT,
MMC is still recognized as MBR.
Invoke part_init() to purge cached data and update
information about partition table type.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/drivers/fastboot/fb_mmc.c b/drivers/fastboot/fb_mmc.c
index 611074a..50532ac 100644
--- a/drivers/fastboot/fb_mmc.c
+++ b/drivers/fastboot/fb_mmc.c
@@ -504,6 +504,7 @@
 				      response);
 			return;
 		}
+		part_init(dev_desc);
 		printf("........ success\n");
 		fastboot_okay(NULL, response);
 		return;
@@ -525,6 +526,7 @@
 				      response);
 			return;
 		}
+		part_init(dev_desc);
 		printf("........ success\n");
 		fastboot_okay(NULL, response);
 		return;