drawable: Fix Phone/Dialer background gradient

The previous framework gradient fix doesn't apply to Phone.apk. This patch gets rid of banding in Phone.apk's background.
Patch-set 2: image credit: @arzbhatia

Signed-off-by: ArmanUV <armansamimi@gmail.com>
Change-Id: Id3257a353dd20afbecfb80b1f221ff9540edeeb5