drm/xe/xe_devcoredump: Check NULL before assignments

Assign 'xe_devcoredump_snapshot *' and 'xe_device *' only if
'coredump' is not NULL.

v2
- Fix commit messages.

v3
- Define variables before code.(Ashutosh/Jose)

v4
- Drop return check for coredump_to_xe. (Jose/Rodrigo)

v5
- Modify misleading commit message. (Matt)

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240328123739.3633428-1-himal.prasad.ghimiray@intel.comSigned-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_devcoredump.c

@@ -77,17 +77,19 @@ static ssize_t xe_devcoredump_read(char *buffer, loff_t offset,
 				   size_t count, void *data, size_t datalen)
 {
 	struct xe_devcoredump *coredump = data;
-	struct xe_device *xe = coredump_to_xe(coredump);
-	struct xe_devcoredump_snapshot *ss = &coredump->snapshot;
+	struct xe_device *xe;
+	struct xe_devcoredump_snapshot *ss;
 	struct drm_printer p;
 	struct drm_print_iterator iter;
 	struct timespec64 ts;
 	int i;
 
-	/* Our device is gone already... */
-	if (!data || !coredump_to_xe(coredump))
+	if (!coredump)
 		return -ENODEV;
 
+	xe = coredump_to_xe(coredump);
+	ss = &coredump->snapshot;
+
 	/* Ensure delayed work is captured before continuing */
 	flush_work(&ss->work);