env_eeprom - fix bus recovery for "eeprom_bus_read"

"env_eeprom_bus" is no longer in use (it was introduced in commit
548738b4 "cmd_eeprom: I2C updates").

As in "eeprom_bus_write" we just reset I2C bus with the one we saved in
"old_bus".

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Wolfgang Denk <wd@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Heiko Schocher <hs@denx.de>