drivers: net: cpsw: fix wrong regs access in cpsw_ndo_open

The cpsw_ndo_open() could try to access CPSW registers before
calling pm_runtime_get_sync(). This will trigger L3 error:

 WARNING: CPU: 0 PID: 21 at drivers/bus/omap_l3_noc.c:147 l3_interrupt_handler+0x220/0x34c()
 44000000.ocp:L3 Custom Error: MASTER M2 (64-bit) TARGET L4_FAST (Idle): Data Access in Supervisor mode during Functional access

and CPSW will stop functioning.

Hence, fix it by moving pm_runtime_get_sync() before the first access
to CPSW registers in cpsw_ndo_open().

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>