media: sti/delta: remove uneeded check

At the error logic, ipc_buf was already asigned to &ctx->ipc_buf_struct,
with can't be null, as warned by smatch:

	drivers/media/platform/sti/delta/delta-ipc.c:223 delta_ipc_open() warn: variable dereferenced before check 'ctx->ipc_buf' (see line 183)

So, remove the uneeded check.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>