[nrf noup] tests: drivers: mspi: api: nRF54L15 fix frequency

nrf-squash! [nrf noup] tests: drivers: mspi: api: Add nRF54L15 overlay file

Fix device frequency for nRF54L15. SDP MSPI allows only a predefined
set of device frequencies.

Signed-off-by: Magdalena Pastula <magdalena.pastula@nordicsemi.no>

Author: magp-nordic

tests/drivers/mspi/api/boards/nrf54l15dk_nrf54l15_cpuapp.overlay

@@ -18,7 +18,7 @@
 			status = "okay";
 			compatible = "zephyr,mspi-emul-device";
 			reg = <0x0>;
-			mspi-max-frequency = <48000000>;
+			mspi-max-frequency = <DT_FREQ_M(1)>;
 		};
 	};
 };