spi/mpc52xx-spi: minor cleanups

- drop own, obsolete include-file
- drop IRQF_SAMPLE_RANDOM (deprecated feature)
- drop 'if' above kfree()
- typos, braces & whitespaces

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Luotao Fu <l.fu@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>