i2cdump: display the numeric value for block read ioctl() errors

This makes busybox i2cdump compatible with the upstream version, which
also displays the numeric error value in case of a block read failure.

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/i2c_tools.c b/miscutils/i2c_tools.c
index 7be4890..e19d851 100644
--- a/miscutils/i2c_tools.c
+++ b/miscutils/i2c_tools.c
@@ -732,8 +732,10 @@
 			tmp = i2c_smbus_read_i2c_block_data(
 					buf_fd, res, I2C_SMBUS_BLOCK_MAX,
 					cblock + res);
-			if (tmp <= 0)
+			if (tmp <= 0) {
+				blen = tmp;
 				goto fail;
+			}
 		}
 
 		if (res >= I2CDUMP_NUM_REGS)
@@ -750,7 +752,7 @@
 	return blen;
 
  fail:
-	bb_error_msg_and_die("block read failed");
+	bb_error_msg_and_die("block read failed: %d", blen);
 }
 
 /* Dump all but word data. */