Linux kernel: RTC driver crashes on unchecked clock error during probe

In the Linux kernel, the following vulnerability has been resolved:

rtc: mpfs: fix unchecked devm_clk_get() error pointer in probe()

devm_clk_get(&pdev->dev, "rtcref")'s return value was passed straight into clk_get_rate() without checking it for an error first, unlike the "rtc" clock a few lines above which is correctly checked with IS_ERR(). clk_get_rate() only guards against a NULL clk, not an error pointer:

if (!clk)
	return 0;
...
rate = clk_core_get_rate_recalc(clk->core);

so if devm_clk_get() ever returns an error pointer here (for example ERR_PTR(-EPROBE_DEFER), which is the normal, expected outcome if the clkcfg clock-provider this RTC depends on has not registered its clocks yet by the time this driver probes), clk_get_rate() dereferences that error pointer instead of returning 0, crashing instead of letting probe defer.

Capture the clock in the existing 'clk' local and check it with IS_ERR() before calling clk_get_rate(), matching the handling already used for the "rtc" clock in this same function.