bnx2x: Check unzip return code

Without this check, when running out of memory, we will see PSOD's in
bnx2x_init_fill() when doing a memset().  This is because at that time,
bp->gunzip_buf is not pointing to a valid allocated space.

Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>