arch/tile: change lower bound on syscall error return to -4095

Previously we were using -1023, which is fine for normal syscall
error returns, but the common value in use for other platforms
is -4095, and one Tilera-specific driver does use values in the
-1100 range, so tickled this bug.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/intvec_32.S

@@ -1020,7 +1020,7 @@ STD_ENTRY(interrupt_return)
 
 	/* Set r1 to errno if we are returning an error, otherwise zero. */
 	{
-	 moveli r29, 1024
+	 moveli r29, 4096
 	 sub    r1, zero, r0
 	}
 	slt_u   r29, r1, r29