serial: ifx6x60: add_timer is not safe in the mrdy_assert function
This patch make use of mod_timer instead of add_timer in the mrdy_assert function.
Because the srdy interrupter can go high when we are running function mrdy_assert and mrdy_assert
can be called by multi-entry. In our medfield platform, spi stress test can encounter this
error logs triggered by the BUG_ON of add_timer function.This patch had been tested on
our medfield platform.
Cc: liu chuansheng <chuansheng.liu@intel.com> Cc: Bi Chao <chao.bi@intel.com> Signed-off-by: Chen Jun <jun.d.chen@intel.com> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>