sensors: tmp112: Fix breakage on stm32f4 platform

It makes no sense to set the restart condition flag on a first message
and some i2c bus drivers (like the stm32 v1 driver) actually reject
them by returning an error from i2c_transfer().

This patch fixes that by using i2c_burst_read() in tmp112_reg_read()
instead. For consistency, tmp112_reg_write() is also changed to use
i2c_burst_write().

Signed-off-by: Mark Vels <mark.vels@team-embedded.nl>