usb: host: ehci-dbg: prefer kmalloc_array over kmalloc times size

This patch fixes a coding style issue reported by checkpatch related to
kmalloc_array usage.

On the same line the sizeof operand was enclosed in parentheses.

Signed-off-by: Geyslan G. Bem <geyslan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>