powerpc/powernv: copy/paste - Mask SO bit in CR

NX can set the 3rd bit in CR register for XER[SO] (Summary overflow)
which is not related to paste request. The current paste function
returns failure for a successful request when this bit is set. So mask
this bit and check the proper return status.

Fixes: 2392c8c8c0 ("powerpc/powernv/vas: Define copy/paste interfaces")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Haren Myneni <haren@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/copy-paste.h

@@ -41,5 +41,6 @@ static inline int vas_paste(void *paste_address, int offset)
 		: "b" (offset), "b" (paste_address)
 		: "memory", "cr0");
 
-	return (cr >> CR0_SHIFT) & CR0_MASK;
+	/* We mask with 0xE to ignore SO */
+	return (cr >> CR0_SHIFT) & 0xE;
 }