i2c: Initialize variable ret

The varialbe `ret` in some functions is not initialized and cause the
build warning and treated as error:

    error: 'ret' may be used uninitialized in this function
    [-Werror=maybe-uninitialized]

Fixes openbmc/phosphor-power#3.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: Ica6b1af434736f6fd96a1bbb9e511bf1c8fb1d7a
diff --git a/tools/i2c/i2c.cpp b/tools/i2c/i2c.cpp
index 4715c6e..7a0bbf4 100644
--- a/tools/i2c/i2c.cpp
+++ b/tools/i2c/i2c.cpp
@@ -200,7 +200,7 @@
 void I2CDevice::read(uint8_t addr, uint8_t& size, uint8_t* data, Mode mode)
 {
     checkIsOpen();
-    int ret;
+    int ret = -1;
     switch (mode)
     {
         case Mode::SMBUS:
@@ -261,7 +261,7 @@
                       Mode mode)
 {
     checkIsOpen();
-    int ret;
+    int ret = -1;
     switch (mode)
     {
         case Mode::SMBUS: