treewide: Fix stale references of Android docs

Commit 9bdf0e8fef86 ("doc: relocate/rename Android README and add BCB
overview") left some obsolete references of Android documents/paths.

This has been pointed out by Sam (thanks!) in:
https://patchwork.ozlabs.org/patch/1104245/#2208134

Fixes: 9bdf0e8fef86 ("doc: relocate/rename Android README and add BCB overview")
Reported-by: Sam Protsenko <semen.protsenko@linaro.org>
Suggested-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 175c6ad..e1e050f 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -735,7 +735,7 @@
 	  Android devices. Fastboot requires either the network stack
 	  enabled or support for acting as a USB device.
 
-	  See doc/README.android-fastboot for more information.
+	  See doc/android/fastboot.txt for more information.
 
 config CMD_FDC
 	bool "fdcboot - Boot from floppy device"