watchdog: fix error in probe() of s3c2410_wdt (reset at booting)

Probe function of s3c2410 watchdog calls request_irq before initializing
required value (wdt_count). This incurs resetting watchdog counter value
and watchdog-reboot during booting up.

This patch addresses such an issue by calling request_irq later.

Error handling in probe function and calling oder in remove function are
also revised accordingly.

Reported-by: Chanwoo Park <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>