nvme-fc: fix the fc_appid_store return value

"nvme-fc: fold t fc_update_appid into fc_appid_store" accidentally
changed the userspace interface for the appid attribute, because the code
that decrements "count" to remove a trailing '\n' in the parsing results
in the decremented value being incorrectly be returned from the sysfs
write.  Fix this by keeping an orig_count variable for the full length
of the write.

Fixes: c814153c83 ("nvme-fc: fold t fc_update_appid into fc_appid_store")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: James Smart <jsmart2021@gmail.com>
Tested-by:  Muneendra Kumar M <muneendra.kumar@broadcom.com>

drivers/nvme/host/fc.c

@@ -3880,6 +3880,7 @@ static int fc_parse_cgrpid(const char *buf, u64 *id)
 static ssize_t fc_appid_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t count)
 {
+	size_t orig_count = count;
 	u64 cgrp_id;
 	int appid_len = 0;
 	int cgrpid_len = 0;
@@ -3904,7 +3905,7 @@ static ssize_t fc_appid_store(struct device *dev,
 	ret = blkcg_set_fc_appid(app_id, cgrp_id, sizeof(app_id));
 	if (ret < 0)
 		return ret;
-	return count;
+	return orig_count;
 }
 static DEVICE_ATTR(appid_store, 0200, NULL, fc_appid_store);
 #endif /* CONFIG_BLK_CGROUP_FC_APPID */