powerpc/fsl: msi: sparse fixes

arch/powerpc/sysdev/fsl_msi.c:31:1: warning: symbol 'msi_head' was not declared. Should it be static?
arch/powerpc/sysdev/fsl_msi.c:138:40: warning: incorrect type in argument 1 (different base types)
arch/powerpc/sysdev/fsl_msi.c:138:40:    expected restricted __be64 const [usertype] *p
arch/powerpc/sysdev/fsl_msi.c:138:40:    got unsigned long long const [usertype] *[assigned] reg

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>