ACPI: APEI: EINJ: Fix check and iounmap of uninitialized pointer p

In the case where a request_mem_region call fails and pointer r is null
the error exit path via label 'out' will check for a non-null pointer
p and try to iounmap it. However, pointer p has not been assigned a
value at this point, so it may potentially contain any garbage value.
Fix this by ensuring pointer p is initialized to NULL.

Fixes: 1a35c88 ("ACPI: APEI: EINJ: Fix kernel test sparse warnings")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://patch.msgid.link/20250624202937.523013-1-colin.i.king@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: ColinIanKing

drivers/acpi/apei/einj-core.c

@@ -401,7 +401,7 @@ static int __einj_error_trigger(u64 trigger_paddr, u32 type,
 	u32 table_size;
 	int rc = -EIO;
 	struct acpi_generic_address *trigger_param_region = NULL;
-	struct acpi_einj_trigger __iomem *p;
+	struct acpi_einj_trigger __iomem *p = NULL;
 
 	r = request_mem_region(trigger_paddr, sizeof(trigger_tab),
 			       "APEI EINJ Trigger Table");