can: hi311x: hi3110_can_probe(): use devm_clk_get_optional() to get the input clock

can: hi311x: hi3110_can_probe(): use devm_clk_get_optional() to get the input clock

It's not clear what was the intention of redundant usage of IS_ERR()
around the clock pointer since with the error check of devm_clk_get()
followed by bailout it can't be invalid,

Simplify the code which fetches the input clock by using
devm_clk_get_optional(). It will allow to switch to device properties
approach in the future.

Link: https://lore.kernel.org/all/20211206165542.69887-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>