esp8266/esp_mphal.h: Fix I2C glitching by using input mode for od_high.
esp8266/esp_mphal.h: Fix I2C glitching by using input mode for od_high.

Certain pins (eg 4 and 5) seem to behave differently at the hardware level
when in open-drain mode: they glitch when set "high" and drive the pin
active high for a brief period before disabling the output driver.  To work
around this make the pin an input to let it float high.

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