ACPI: LPSS: Replace loop with first entry retrieval

After the commit 6505e452371d ("ACPI: LPSS: Use the helper
acpi_dev_get_memory_resources()") the list is empty or
contains only resource of IORESOURCE_MEM type. Hence, no
need to check for the type, and since we break after the
first found, no need to iterate over full list. That said,
replace loop with first entry retrieval.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>