clk: imx: pllv2: avoid using uninitialized values

Forward the errors returned by __clk_pllv2_set_rate() in the recalc rate
function, to avoid using uninitialized values for the rate calculation.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>