lib: shell: replace strtol with strtoul in cmd_load for address parsing

Addresses in cmd_load() should always be unsigned. Previously, strtol()
was used, which is limited to signed long values, causing issues with
addresses >= 0x80000000. This commit replaces strtol() with strtoul(),
ensuring proper handling of the full 32-bit address space.

Fixes #81343

Signed-off-by: Aaron Fontaine <aaron.fontaine@dojofive.com>
Signed-off-by: Jakub Rzeszutko <jakub.rzeszutko@verkada.com>

subsys/shell/modules/devmem_service.c

@@ -247,8 +247,8 @@ static int cmd_load(const struct shell *sh, size_t argc, char **argv)
 		argc--;
 	}
 
-	bytes = (unsigned char *)strtol(argv[1], NULL, 0);
-	data = (uint32_t *)strtol(argv[1], NULL, 0);
+	bytes = (unsigned char *)strtoul(argv[1], NULL, 0);
+	data = (uint32_t *)strtoul(argv[1], NULL, 0);
 
 	set_bypass(sh, bypass_cb);
 	return 0;