doxygen fixes: change @var to @param var

These files were trying to document the parameters, but didn't have
the syntax quite right.  Change the comments from @varname to
@param varname as required by doxygen.

Change-Id: I63662094d3f1686e3e35b61925b580eb06e72e28
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: http://review.coreboot.org/8100
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

src/soc/qualcomm/ipq806x/timer.c

@@ -50,7 +50,7 @@ void init_timer(void)
 
 /**
  * udelay -  generates micro second delay.
- * @usec: delay duration in microseconds
+ * @param usec: delay duration in microseconds
  *
  * With 32KHz clock, minimum possible delay is 31.25 Micro seconds and
  * its multiples. In Rumi GPT clock is 32 KHz