ARM: davinci: don't mark vpif_input structures as 'const'

A change to the platform data definitions caused a warning in the board code:

arch/arm/mach-davinci/board-da850-evm.c:1221:13: warning: initialization discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
arch/arm/mach-davinci/board-da850-evm.c:1231:13: warning: initialization discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]

This is a bit unfortunate, since we generally like structure definitions to
be const, but as this is legacy code, the easiest way out is still to
remove the 'const' annotation here.

Fixes: 4a5f8ae5 ("[media] davinci: vpif_capture: get subdevs from DT when available")
Fixes: 231ce279 ("ARM: davinci: fix const warnings")
Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>