xhci: remove unnecessary boolean parameter from xhci_alloc_command

commands with input contexts are allocated with the
xhci_alloc_command_with_ctx helper.

No functional changes

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>