usb: CONFIG_USB_FASTBOOT prefix replacement for consistency

FASTBOOT is defined both by CONFIG_USB_FUNCTION_FASTBOOT AND CONFIG_CMD_FASTBOOT, so it doesn't
make much sense to have a CONFIG_USB_FASTBOOT prefix for fastboot-specific options, especially
given that other config options for fastboot use the CONFIG_FASTBOOT prefix.

This replaces the CONFIG_USB_FASTBOOT prefix with CONFIG_FASTBOOT, for consistency.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
diff --git a/include/configs/dra7xx_evm.h b/include/configs/dra7xx_evm.h
index 62330bf..7499447 100644
--- a/include/configs/dra7xx_evm.h
+++ b/include/configs/dra7xx_evm.h
@@ -92,8 +92,8 @@
 #define CONFIG_USB_FUNCTION_FASTBOOT
 #define CONFIG_CMD_FASTBOOT
 #define CONFIG_ANDROID_BOOT_IMAGE
-#define CONFIG_USB_FASTBOOT_BUF_ADDR    CONFIG_SYS_LOAD_ADDR
-#define CONFIG_USB_FASTBOOT_BUF_SIZE    0x2F000000
+#define CONFIG_FASTBOOT_BUF_ADDR    CONFIG_SYS_LOAD_ADDR
+#define CONFIG_FASTBOOT_BUF_SIZE    0x2F000000
 #define CONFIG_FASTBOOT_FLASH
 #define CONFIG_FASTBOOT_FLASH_MMC_DEV   1
 #endif