ARM: omap2: make omap5_erratum_workaround_801819 static

Fix sparse warning:

arch/arm/mach-omap2/omap-smp.c:75:6: warning: symbol
'omap5_erratum_workaround_801819' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ma Feng <mafeng.ma@huawei.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>