libdvbv5: Fix build error with hardening build flags

libdvbv5: Fix build error with hardening build flags

On Debian and Ubuntu the following hardening flags are used:
(see dpkg-buildflags --export=sh)

export CFLAGS="-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security"
export CPPFLAGS="-D_FORTIFY_SOURCE=2"
export CXXFLAGS="-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security"
export FFLAGS="-g -O2"
export LDFLAGS="-Wl,-z,relro"

Without this commit the following error occurs:

dvb-fe.c:56:3: error: format not a string literal and no format arguments [-Werror=format-security]
dvb-fe.c:61:3: error: format not a string literal and no format arguments [-Werror=format-security]

Signed-off-by: Gregor Jasny <gjasny@googlemail.com>