media: venus: Fix uninitialized variable count being checked for zero

In the case where plat->codecs is NULL the variable count is uninitialized
but is being checked to see if it is 0. Fix this by initializing
count to 0.

Addresses-Coverity: ("Uninitialized scalar variable")

Fixes: e2992926 ("media: venus: Get codecs and capabilities from hfi platform")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>