staging: bcm: nvm.c: Cleaning up a array that is filled incompletely

Array 'SigBuff' is filled incompletely.
Someone forget to multiply for the sizeof type.

This was partly found using a static code analysis program called cppcheck.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>