spi: ftssp010_spi: Simplify code flow in ftssp010_[wait|wait_tx|wait_rx]

No functional change, just simplify the code a bit.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>