staging: vc04_services: Prefer WARN_ON_ONCE instead of if condition followed by BUG.

staging: vc04_services: Prefer WARN_ON_ONCE instead of if condition followed by BUG.

Coccinelle suggested to use BUG_ON instead of if condition followed by BUG
but BUG_ON should be used in situations where integrity of the system is no
longer guaranteed. In this case, as suggested by Stefan Wahren, vchiq isn't
critical.
Since it is not critical, BUG_ON should be avoided.
Replaced if condition followed by BUG with WARN_ON_ONCE.

Signed-off-by: Kishore KP <kishore.p@techveda.org>
Signed-off-by: Suniel Mahesh <sunil.m@techveda.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>