drivers: rmnet_shs: Change rmnet_port init

Rmnet_port was being collected previously from
the first saved instance of a phy_dev into a temporary variable.
This could cause issue if the phy_dev was incorrectly made.

This change causes the phy_dev to be collected at the time of
initialization when the 1st rmnet is brought up.

<6> Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b6b
<6> Mem abort info:
<6>   Exception class = DABT (current EL), IL = 32 bits
<6>   SET = 0, FnV = 0
<6>   EA = 0, S1PTW = 0
<6>   FSC = 4
<6> Data abort info:
<6>   ISV = 0, ISS = 0x00000004
<6>   CM = 0, WnR = 0
<6> [006b6b6b6b6b6b6b] address between user and kernel address ranges
<6> Internal error: Oops: 96000004 [#1] PREEMPT SMP
<2> Call trace:
<2>  rmnet_map_dl_ind_deregister+0x3c/0x84
<2>  rmnet_shs_exit+0x40/0x74 [rmnet_shs]
<2>  rmnet_shs_dev_notify_cb+0x100/0x48c [rmnet_shs]
<2>  notifier_call_chain+0x8c/0xd0
<2>  raw_notifier_call_chain+0x38/0x48
<2>  call_netdevice_notifiers_info+0x40/0x70
<2>  __dev_close_many+0x64/0x108
<2>  dev_close_many+0x88/0x138
<2>  rollback_registered_many+0x138/0x434
<2>  rollback_registered+0x5c/0xa0
<2>  unregister_netdevice_queue+0x94/0xac
<2>  unregister_netdev+0x24/0x34

Change-Id: Idc2b3059cbcb9c1ccb1091c630d27bdcdc0e894d
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>