[ARM] vfp: fix leak of VFP_NAN_FLAG into FPSCR

The VFP code can leak VFP_NAN_FLAG into the FPSCR. It doesn't correspond
to any real FPSCR bit (and overlaps one of the exception flags).

Bug report from Daniel Jacobowitz

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index 22f3da4..37ff814 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -180,7 +180,7 @@
 		 * emulate it.
 		 */
 	}
-	return exceptions;
+	return exceptions & ~VFP_NAN_FLAG;
 }
 
 /*