set but not used variables
shadowing a previous local

A hidden problem was that the VERIFY_RR_* macros define local 'rc'
variables, any other local definitions for those would be shadowed and
generate warnings from gcc. I've renamed the other locals 'ret'
instead of 'rc'.
Signed-off-by: Keith Packard <keithp@keithp.com>

Backported from Arctica GH 3.6.x branch.

v2: backport to nx-libs 3.6.x (Ulrich Sibiller)
v3: backport to nx-libs 3.5.0.x (Mihai Moldovan)