pstore: fix one type of return value in pstore

the return type of function _read_ in pstore is size_t,
but in the callback function of _read_, the logic doesn't
consider it too much, which means if negative value (assuming
error here) is returned, it will be converted to positive because
of type casting. ssize_t is enough for this function.

Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index f835a25..912403c 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -152,7 +152,7 @@
 void pstore_get_records(void)
 {
 	struct pstore_info *psi = psinfo;
-	size_t			size;
+	ssize_t			size;
 	u64			id;
 	enum pstore_type_id	type;
 	struct timespec		time;
@@ -163,7 +163,7 @@
 
 	mutex_lock(&psinfo->buf_mutex);
 	while ((size = psi->read(&id, &type, &time)) > 0) {
-		if (pstore_mkfile(type, psi->name, id, psi->buf, size,
+		if (pstore_mkfile(type, psi->name, id, psi->buf, (size_t)size,
 				  time, psi->erase))
 			failed++;
 	}