cxgb4: fix sleep in atomic when flashing PHY firmware

Before writing new PHY firmware to on-chip memory, driver queries
firmware for current running PHY firmware version, which can result
in sleep waiting for reply. So, move spinlock closer to the actual
on-chip memory write operation, instead of taking it at the callers.

Fixes: 5fff701c ("cxgb4: always sync access when flashing PHY firmware")
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>