commit aaedb9e0 upstream.

Since a few kernel releases the Pogoplug 4 has crashed like this
during boot:

Unable to handle kernel NULL pointer dereference at virtual address 00000002
(...)
[<c04116ec>] (strlen) from [<c00ead80>] (kstrdup+0x1c/0x4c)
[<c00ead80>] (kstrdup) from [<c04591d8>] (__clk_register+0x44/0x37c)
[<c04591d8>] (__clk_register) from [<c04595ec>] (clk_hw_register+0x20/0x44)
[<c04595ec>] (clk_hw_register) from [<c045bfa8>] (__clk_hw_register_mux+0x198/0x1e4)
[<c045bfa8>] (__clk_hw_register_mux) from [<c045c050>] (clk_register_mux_table+0x5c/0x6c)
[<c045c050>] (clk_register_mux_table) from [<c0acf3e0>] (kirkwood_clk_muxing_setup.constprop.0+0x13c/0x1ac)
[<c0acf3e0>] (kirkwood_clk_muxing_setup.constprop.0) from [<c0aceae0>] (of_clk_init+0x12c/0x214)
[<c0aceae0>] (of_clk_init) from [<c0ab576c>] (time_init+0x20/0x2c)
[<c0ab576c>] (time_init) from [<c0ab3d18>] (start_kernel+0x3dc/0x56c)
[<c0ab3d18>] (start_kernel) fro...