reset: fix of_reset_simple_xlate kerneldoc comment

The flags parameter never made it into the API, but was erroneously
included in the kerneldoc comment. Remove it to fix a documentation
build warning:

  ./drivers/reset/core.c:86: warning: Excess function parameter 'flags' description in 'of_reset_simple_xlate'

Fixes: 61fc4131 ("reset: Add reset controller API")
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>