ata: pata_arasan: Staticize local symbols

These local symbols are used only in this file.
Fix the following sparse warnings:

drivers/ata/pata_arasan_cf.c:657:6: warning: symbol 'arasan_cf_error_handler' was not declared. Should it be static?
drivers/ata/pata_arasan_cf.c:686:14: warning: symbol 'arasan_cf_qc_issue' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>