i2c: ismt: Use minimum descriptor size

Software is allowed to allocate number of descriptor size from 2 to 256,
this i2c controller could process more descriptor, but for i2c core soft
ware layer, only one i2c transaction is allowed each time.

So here switch to minimum 2 descriptor when initialization.
Signed-off-by: Fan Du <fan.du@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-ismt.c

@@ -81,7 +81,7 @@
 #define PCI_DEVICE_ID_INTEL_S1200_SMT1	0x0c5a
 #define PCI_DEVICE_ID_INTEL_AVOTON_SMT	0x1f15
 
-#define ISMT_DESC_ENTRIES	32	/* number of descriptor entries */
+#define ISMT_DESC_ENTRIES	2	/* number of descriptor entries */
 #define ISMT_MAX_RETRIES	3	/* number of SMBus retries to attempt */
 
 /* Hardware Descriptor Constants - Control Field */