platform/x86: intel/pmc: Fix ioremap() of bad address

In pmc_core_ssram_get_pmc(), the physical addresses for hidden SSRAM
devices are retrieved from the MMIO region of the primary SSRAM device.
If additional devices are not present, the address returned is zero.
Currently, the code does not check for this condition, resulting in
ioremap() incorrectly attempting to map address 0.

Add a check for a zero address and return 0 if no additional devices
are found, as it is not an error for the device to be absent.

Fixes: a01486d ("platform/x86/intel/pmc: Cleanup SSRAM discovery")
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20250106174653.1497128-1-david.e.box@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: debox1

drivers/platform/x86/intel/pmc/core_ssram.c

@@ -269,8 +269,12 @@ pmc_core_ssram_get_pmc(struct pmc_dev *pmcdev, int pmc_idx, u32 offset)
 		/*
 		 * The secondary PMC BARS (which are behind hidden PCI devices)
 		 * are read from fixed offsets in MMIO of the primary PMC BAR.
+		 * If a device is not present, the value will be 0.
 		 */
 		ssram_base = get_base(tmp_ssram, offset);
+		if (!ssram_base)
+			return 0;
+
 		ssram = ioremap(ssram_base, SSRAM_HDR_SIZE);
 		if (!ssram)
 			return -ENOMEM;