9p: Fix sparse error

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/net/9p/trans_common.c b/net/9p/trans_common.c
index d47880e..e883172 100644
--- a/net/9p/trans_common.c
+++ b/net/9p/trans_common.c
@@ -66,7 +66,7 @@
 	uint32_t pdata_mapped_pages;
 	struct trans_rpage_info  *rpinfo;
 
-	*pdata_off = (size_t)req->tc->pubuf & (PAGE_SIZE-1);
+	*pdata_off = (__force size_t)req->tc->pubuf & (PAGE_SIZE-1);
 
 	if (*pdata_off)
 		first_page_bytes = min(((size_t)PAGE_SIZE - *pdata_off),