mwifiex: skip firmware dump when read_regs() fails

If we are not able to read registers or PCIe memory,
it means PCIe device is in bad state. We will skip
firmware dump in this case.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>