staging: vchiq_core: drop extern prefix in function declarations

Remove unnecessary extern prefix in function declarations.

While at it, remove a now outdated comment and realign the function
declarations in order to improve readability.

Signed-off-by: Gaston Gonzalez <gascoar@gmail.com>
Link: https://lore.kernel.org/r/20211024212524.370078-7-gascoar@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>