cmake: fix to allow reconfiguring install prefix
uhd: fix GRC wrapper generation to match UHD change (fixes #562)

From: Timo Juhani Lindfors <timo.lindfors@iki.fi>
Date: Tue, 9 Jul 2013 09:23:06 +0300
Subject: [PATCH] uhd: "scalar" stream arg is now called "peak"

uhd commit d46c176af34b728fd43b3dd46485b38623a7335e (dsp rework: tx
trailer, scaling work (peak)) renamed "scalar" stream arg to "peak"
and changed its semantics. Using 1/256=.003906 captures upper 8-bits.