cxl/pci: simplify the check of mem_enabled in cxl_hdm_decode_init()

cxl/pci: simplify the check of mem_enabled in cxl_hdm_decode_init()

Cases can be divided into two categories which are DVSEC range enabled and
not enabled when HDM decoders exist but is not enabled. To avoid checking
info->mem_enabled, which indicates the enablement of DVSEC range, every
time, we can check !info->mem_enabled once in advance. This simplification
can make the code clearer.

No functional change intended.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Yanfei Xu <yanfei.xu@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20240828084231.1378789-5-yanfei.xu@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>