clocksource: samsung_pwm_timer: Use proper clockevents max_delta

This patch replaces hardcoded -1 argument passed to
clockevents_config_and_register() with tcnt_max calculated based on
variant data.

This fixes invalid max delta configuration for 16-bit timers of s3c24xx.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Olof Johansson <olof@lixom.net>