can: flexcan: flexcan_clks_enable(): add missing variable initialization

This patch adds the missing initialization of the "err" variable in
the flexcan_clks_enable() function.

Fixes: d9cead75 ("can: flexcan: add mcf5441x support")
Link: https://lore.kernel.org/r/20210728075428.1493568-1-mkl@pengutronix.de


Reported-by: kernel test robot <lkp@intel.com>
Cc: Angelo Dureghello <angelo@kernel-space.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>