classes/externalsrc: fix setting of deps varflag as a string
The value of the deps varflag for tasks is (unusually) expected to be a
list object rather than a space-separated string, hence we cannot use
appendVarFlag() here. This fixes a traceback when parsing the gcc recipe
with externalsrc enabled, for example.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
