ar71xx-generic: fix DIR825C1

Build failed with:
 * unable to set 'CONFIG_TARGET_DEVICE_PACKAGES_ar71xx_generic_DEVICE_dir-825-c1
 * unable to enable device 'dir-825-c1'

This was likely because the device is defined in
target/linux/ar71xx/image/generic-legacy-devices.mk as DIR825C1 and
hence needs 'profile' to be set.

targets/ar71xx-generic

@@ -103,7 +103,9 @@ device('d-link-dir-825-rev-b1', 'dir-825-b1', {
 	class = 'tiny', -- Only 6M of usable Firmware space
 })
 
-device('d-link-dir-825-rev-c1', 'dir-825-c1')
+device('d-link-dir-825-rev-c1', 'dir-825-c1', {
+	profile = 'DIR825C1'
+})
 
 
 -- GL.iNet