ARM: SAMSUNG: fix race in s3c_adc_start for ADC

Checking for adc->ts_pend already claimed should be done with the
lock held.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>