greybus: manifest: convert pr_err to dev_err

This patch converts a dangling pr_err in the manifest parsing error path to
a dev_err in order to remain consistent with similar error messages
elsewhere.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>