ACPI, APEI, Fix acpi_pre_map() return value

After we ioremap() a new region, we call __acpi_try_ioremap() to
see whether another thread has already mapped the same region.
This check clobbers "vaddr",  so compute the return value of
acpi_pre_map() using the ioremap() result "map->vaddr" instead.

v2:
    Modified the unsuitable description of patch.

v3:
    Removed unlikely() check and made description simpler.

Signed-off-by: Jin Dongming <jin.dongming@np.css.fujitsu.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>