gui: fix DEVICE_RESOLUTION warnings in Android.mk

Indenting the warnings with tab resulted in a make error
"*** commands commence before first target.  Stop."
instead of the intended message. Using spaces instead.

Also fixed the web link to point to the current build guide on XDA
instead of the outdated one on rootzwiki.

Change-Id: I8b25d39edae16dbc479c0e36bd11e12b49b4fbb0