[S390] hvc_iucv: do not call iucv_unregister if iucv_register failed

If the iucv_register() functions fails, the error recovery calls
iucv_unregister() which might cause the following stack backtrace:

	(<0000000000100ab2> show_trace+0xee/0x144)
	<00000000004f1842> panic+0xb6/0x248
	<00000000001010a6> die+0x15a/0x16c
	<000000000011d936> do_no_context+0xa6/0xe4
	<00000000004f84dc> do_protection_exception+0x2e8/0x3a4
	<0000000000113afc> pgm_exit+0x0/0x14
	<00000000004e786e> iucv_unregister+0x5a/0x17c
	(<00000000004e785e> iucv_unregister+0x4a/0x17c)
	<000000000076de74> hvc_iucv_init+0x228/0x5dc
	<00000000001000c2> do_one_initcall+0x3e/0x19c
	<00000000007524a2> kernel_init+0x28e/0x404
	<0000000000105dd6> kernel_thread_starter+0x6/0xc
	<0000000000105dd0> kernel_thread_starter+0x0/0xc

Remove the call to iucv_unregister() and remove the goto label
as unregistering is the last step in the hvc_iucv initialization.
If iucv_register() fails, simply clean up hvc terminals and free
resources.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>