fs: shell: Fix FS shell using fixed storage_partition name instead of DT

[joerchan]

Fix FS shell using fixed 'storage_partition' nodelabel instead of accessing the DT defined partition from the zephyr,fstab,littlefs node partition property.

Reproduce issue:

west build  -b nucleo_h7a3zi_q samples/subsys/fs/littlefs \
-- \
-DCONFIG_FILE_SYSTEM_SHELL=y \
-DCONFIG_SHELL=y \
-DCONFIG_HEAP_MEM_POOL_SIZE=1024

Compare these two boards partitions:

nucleo_h7a3zi_q.overlay:

/ {
	fstab {
		compatible = "zephyr,fstab";
		lfs1: lfs1 {
			compatible = "zephyr,fstab,littlefs";
			partition = <&lfs1_partition>;
                };
	};
};

&flash0 {
	partitions {
		compatible = "fixed-partitions";
		lfs1_partition: partition@100000 {
			label = "storage";
			reg = <0x100000 DT_SIZE_K(1024)>;
		};
	};
};

nucleo_h743zi.overlay

/ {
	fstab {
		compatible = "zephyr,fstab";
		lfs1: lfs1 {
			compatible = "zephyr,fstab,littlefs";
			partition = <&storage_partition>;
		};
	};
};

&quadspi {
	mx25l25645g: qspi-nor-flash@90000000 {
		compatible = "st,stm32-qspi-nor";
		partitions {
			   compatible = "fixed-partitions";
			   storage_partition: partition@0 {
			       label = "storage";
			       reg = <0 DT_SIZE_M(8)>;
			   };
		};
	};
};

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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