staging/sep: Fix smatch false positive about potential NULL dereference in sep_main.c

Smatch complains about a potential NULL pointer dereference:

sep_main.c:2312 sep_construct_dma_tables_from_lli() error: potential
NULL dereference 'info_out_entry_ptr'.

info_out_entry_ptr is initialized with NULL and if info_in_entry_ptr is
not NULL it gets derefenced.
However info_out_entry_ptr is only NULL in the first iteration of the
while loop and in this case info_in_entry_ptr is also NULL (as indicated
by the comment /* If info entry is null - this is the first table built */
-> this is a false positive.

Nevertheless we add a check for info_out_entry_ptr to silence this
warning and make it more robust in regard to code changes.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>