ARM: OMAP: omap_uwire: wait for tx complete before starting the next one

The TDR register shouldn't be written when the CSRB flag is set. The fix
solves the problem where one SPI transfer includes multiple 8 or 16 bit
tx elements and the current transfer can be corrupted by accessing the
TDR too early.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>