clocksource: samsung_pwm_timer: Drop unused samsung_pwm struct

This patch removes the unused samsung_pwm struct from public header.

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>