infcall: remove unused parameter in 'value_arg_coerce'

Remove the unused SP parameter from the auxiliary function
'value_arg_coerce'.

gdb/ChangeLog:
2019-10-23  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* infcall.c (value_arg_coerce): Remove an unused parameter.
	(call_function_by_hand_dummy): Update the call to
	'value_arg_coerce'.

Change-Id: If324a1dda3fa5d4c145790b92bd3f656c00296f4