[media] em28xx: use a better value for I2C timeouts

In the lack of a better spec, let's assume the timeout
values compatible with SMBus spec:
	http://smbus.org/specs/smbus110.pdf

at chapter 8 - Electrical Characteristics of SMBus devices

Ok, SMBus is a subset of I2C, and not all devices will be
following it, but the timeout value before this patch was not
even following the spec.

So, while we don't have a better guess for it, use 35 + 1
ms as the timeout.
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx.h

@@ -183,8 +183,21 @@
 
 #define EM28XX_INTERLACED_DEFAULT 1
 
-/* time in msecs to wait for i2c writes to finish */
-#define EM2800_I2C_XFER_TIMEOUT		20
+/*
+ * Time in msecs to wait for i2c xfers to finish.
+ * 35ms is the maximum time a SMBUS device could wait when
+ * clock stretching is used. As the transfer itself will take
+ * some time to happen, set it to 35 ms.
+ *
+ * Ok, I2C doesn't specify any limit. So, eventually, we may need
+ * to increase this timeout.
+ *
+ * FIXME: this assumes that an I2C message is not longer than 1ms.
+ * This is actually dependent on the I2C bus speed, although most
+ * devices use a 100kHz clock. So, this assumtion is true most of
+ * the time.
+ */
+#define EM28XX_I2C_XFER_TIMEOUT		36
 
 /* time in msecs to wait for AC97 xfers to finish */
 #define EM28XX_AC97_XFER_TIMEOUT	100