mtd: s3c2410: Use devm_* functions

devm_* functions are device managed functions and make cleanup code
simpler and smaller.
devm_kzalloc, devm_clk_get and devm_request_and_ioremap functions
are used.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>