staging: gdm72xx: Replace timeval with ktime_t

struct sdu_stamp in the gdm_sdio.h is a timeval type.
'struct timeval now' is used for calculating elapsed time.

32-bit systems using 'struct timeval' will break in the year 2038,
so we have to replace that code with more appropriate types.
This patch changes the gdm72xx driver to use ktime_t.

ktime_get() is  better than using do_gettimeofday(),
because it uses the monotonic clock. ktime_sub
are used to subtract two ktime variables.

Build tested this by saying Y to WIMAX_GDM72XX.

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>